Method for determining a position of a magnetic source

ABSTRACT

A method for determining a position of a magnetic source includes measuring a magnetic field generated by the magnetic source and determining components of the three-dimensional magnetic flux density of the magnetic field at a plurality of points in space based on such measurement. The method also includes estimating a position of the magnetic source and determining components of a theoretical three-dimensional magnetic flux density at the plurality of points in space based on the estimated position. The position of the magnetic source may then be determined by minimizing the difference between the components of the measured and corresponding theoretical three-dimensional magnetic flux density components.

CROSS-REFERENCE TO RELATED U.S. PATENT APPLICATION

Cross-reference is made to U.S. Utility Patent application Ser. No.______ entitled “SYSTEM AND METHOD FOR REGISTERING A BONE OF A PATIENTWITH A COMPUTER ASSISTED ORTHOPAEDIC SURGERY SYSTEM,” which was filed onDec. 30, 2005 by Jason T. Sherman et al., to U.S. Utility Patentapplication Ser. No. ______ entitled “APPARATUS AND METHOD FORREGISTERING A BONE OF A PATIENT WITH A COMPUTER ASSISTED ORTHOPAEDICSURGERY SYSTEM,” which was filed on Dec. 30, 2005 by Jason T. Sherman etal., and to U.S. Utility Patent application Ser. No. ______ entitled“MAGNETIC SENSOR ARRAY,” which was filed on Dec. 30, 2005 by Jason T.Sherman et al., the entirety of all of which is expressly incorporatedherein by reference.

TECHNICAL FIELD

The present disclosure relates generally to computer assisted surgerysystems for use in the performance of orthopaedic procedures.

BACKGROUND

There is an increasing adoption of minimally invasive orthopaedicprocedures. Because such surgical procedures generally restrict thesurgeon's ability to see the operative area, surgeons are increasinglyrelying on computer systems, such as computer assisted orthopaedicsurgery (CAOS) systems, to assist in the surgical operation.

Computer assisted orthopaedic surgery (CAOS) systems assist surgeons inthe performance of orthopaedic surgical procedures by, for example,displaying images illustrating surgical steps of the surgical procedurebeing performed and rendered images of the relevant bones of thepatient. Before a computer assisted orthopaedic surgery (CAOS) systemcan display a rendered image of a bone, the bone must first beregistered with the computer assisted orthopaedic surgery (CAOS) system.Registering the bone with the computer assisted orthopaedic surgery(CAOS) system allows the system to determine the relevant contour,location, and orientation of the bone and display the rendered imageaccording to such parameters. In typical computer assisted orthopaedicsurgery (CAOS) systems, a bone is registered by touching a number oflocations of the bone with a probe. In response, the system computes arendered image of the bone, including the contour of the bone, based onthe recorded locations. Because the typical registration process occursduring the orthopaedic surgery procedure, the typical registrationprocess may add additional surgery time and increase the time duringwhich the patient is exposed to possible infection. Moreover, currentregistration of the bony anatomy of particular skeletal areas, such asthe hip joint, are challenging due to the difficulty of fiducial markersand anatomical planes.

SUMMARY

According to one aspect, a method for operating a computer assistedorthopaedic surgery system includes determining a position of a magneticsource coupled to a bone of a patient. The position of the magneticsource may be determined based on a magnetic field generated by themagnetic source. Determining a position of the magnetic source mayinclude sensing the magnetic field. For example, determining a positionof the magnetic source may include sensing a three dimensional magneticflux density or portion thereof. The magnetic source may include one ormore magnets. For example, the magnetic source may include acylindrical, dipole magnet(s). The magnetic source may be coupled to thebone via implanting the magnetic source into the bone. The magneticsource may be implanted using a jig. In embodiments wherein the magneticsource includes two or more magnets, the magnets may be implanted at anyorientation relative to each other. For example, the magnets may beimplanted orthogonal to each other. Additionally, the magnets may beimplanted a distance apart from each other such that the individualmagnetic fields do not substantially interfere with each other. Forexample, the magnets may be implanted two times or more the maximumsensing distance of a magnet sensor or collection of magnetic sensorssuch as, a magnetic sensor array.

The magnetic sensor array may be embodied as one or more magneticsensors. The magnetic sensors may measure the scalar components ormagnitude of any or all components of the three-dimensional magneticflux density of the magnetic field of the magnetic source at a point inspace (i.e., the location of the magnetic source). The magnetic sensorarray may also include a housing for positioning the magnetic sensors inthe magnetic field of the magnetic source(s). The magnetic sensor arraymay further include a processing circuit electrically coupled to themagnetic sensors and configured to determine position data indicative ofthe position of the magnetic source relative to the magnetic sensorarray. For example, the processing circuit may be configured todetermine a number of coefficients indicative of the six degrees offreedom of the magnetic source. To do so, the magnetic sensor array maydetermine an initial estimate of the position of the magnetic source.Based on the initial estimate, the magnetic sensor array may determineone or more components of the theoretical magnetic flux density of themagnetic source. The magnetic sensor array may also determine a sum oferrors between the theoretical and measured values of the magnetic fluxdensity. The magnetic sensor array may be also be configured to optimizethe sum of error by determining a new estimate for the position of themagnetic source using a global or local optimization algorithm.

The magnetic sensor array may also include a transmitter, such as awireless transmitter, electrically coupled to the processing circuit fortransmitting position data to, for example, a controller or computer ofa CAOS system. The magnetic sensor array may also include an indicator,such as a visual indicator, that is activated by the processing circuitwhile the magnetic flux density sensed by the magnetic sensors is abovea predetermined threshold value. The magnetic sensor array may furtherinclude a register button selectable by a user to cause the magneticsensor array to transmit sensory data to the controller via, forexample, the wireless transmitter. A reflective sensor array may also becoupled to the magnetic sensor array. Via cooperation of the reflectivesensor array and a camera of the computer assisted orthopaedic surgery(CAOS) system, the position of the magnetic sensor array relative to thecomputer assisted orthopaedic surgery (CAOS) system can be determined.

Output signals of the magnetic sensor array (e.g., of the magneticsensor(s)) may be adjusted to account for environmental magnetic fieldssuch as the Earth's magnetic field and/or offset biases of the magneticsensors included in the magnetic sensor array. Further, the measurementsof the magnetic sensor array may be verified prior to the registrationprocess or as part of a maintenance process by use of a test apparatushaving a test magnetic source of known magnetic strength or flux densityand distance from the magnetic sensor array.

The method may also include determining position data indicative of aposition of the magnetic source based on the magnetic field. Determiningposition data may include determining a position of the magnetic sourcerelative to a magnetic sensor array and/or determining a position of amagnetic sensor array relative to the computer assisted orthopaedicsurgery (CAOS) system. Determining position data may also includedetermining values of the six degrees of freedom of the magnetic source(i.e., three orthogonal spatial coordinates and three angles of rotationabout each orthogonal axis).

The method may further include retrieving an image of the bone from adatabase or other storage location. The image may be any type ofpre-generated three-dimensional image of the bone including indicia ofthe relative position of the magnetic source (e.g., the position of themagnet(s)). The method may include determining a positionalrelationship, such as a vector, between the bone and the magneticsource. The method may yet further include creating a graphicallyrendered image of the bone based on the retrieved image, the positiondata, and the positional relationship between the bone and the magneticsource. The graphically rendered image of the bone may include surfacecontours determined based on the image data. The graphically renderedimage may be displayed in a location and orientation based on theposition data. The method may also include locating the magnetic sourcewith a magnetic sensor array after the creating step. The magneticsource may then be decoupled from the bone after it is located with themagnetic sensor array.

According to another aspect, a computer assisted surgery system includesa display device, a processor electrically coupled to the displaydevice, and a memory device electrically coupled to the processor. Thememory device may have stored therein a plurality of instructions, whichwhen executed by the processor, may cause the processor to receiveposition data indicative of a position of a magnetic source coupled to abone of a patient. The position data may be received (e.g., wirelesslyreceived) from a magnetic sensor array. The plurality of instructionsmay also cause the processor to determine a position of the magneticsensor array relative to a reference point such as a camera orcontroller of the system. The plurality of instructions may furthercause the processor to retrieve an image of the bone of the patient froma database and display a graphically rendered image of the bone on thedisplay device in a location and orientation based on the retrievedimage and the determining step.

According to a further aspect, a method for registering a bone with aCAOS system may include coupling a magnetic source to a bone of thepatient. As discussed above, the magnetic source may include one or moremagnets such as, for example, cylindrical, dipole magnets. The magneticsource may be coupled to the bone by implanting the magnetic source inthe bone. In embodiments wherein the magnetic source includes two ormore magnets, a jig may be used to couple the magnets to the bone. Themagnets may be coupled to the bone at a predetermined angle with respectto each other. Alternatively, the two or more magnets may be coupled toeach other with a support member such that their position (location andorientation) relative to each other is fixed. In addition, the magnetsmay be coupled at a distance from each other such that the individualmagnetic fields of each magnet do not substantially interfere with themagnetic field of other magnets which form the magnetic source. Forexample, in some embodiments, the magnets are coupled a distance fromeach other that is at least twice the distance of the desired maximumsensing distance for the magnetic source.

The method may also include generating an image of the bone subsequentto the coupling step. The image may include indicia of the position ofthe magnetic source relative to the bone. The method may further includedetermining a position of the magnetic source based on a magnetic fieldgenerated by the magnetic source. The method may yet further includecreating a graphically rendered image of the bone based on the retrievedimage, the position data, and a positional relationship between the boneand the magnetic source. The graphically rendered image of the bone mayinclude surface contours determined based on the image data. Thegraphically rendered image may be displayed in a location andorientation based on the position data. The method may also includelocating the magnetic source with a magnetic sensor array after thecreating step. The magnetic source may then be decoupled from the boneafter the bone has been registered with the computer assistedorthopaedic surgery (CAOS) system.

According to yet a further aspect, an apparatus for registering a boneof a patient with a CAOS system may include a support frame, a firstmagnetic sensor array coupled to the support frame, and a secondmagnetic sensor array coupled to the support frame. In some embodiments,the apparatus may include more or less magnetic sensor arrays. Each ofthe magnetic sensor arrays are movable with respect to the supportframe. For example, each magnetic sensor array may be pivoted and/ortranslated with respect to the frame. Each magnetic sensor arrayincludes a circuit configured to sense a magnetic field of a magneticsource and determine position data indicative a position of the magneticsource. The circuit may include, for example, one or more magneticsensors and a processing circuit. The circuit may further include anangle sensor configured to determine an angle defined between themagnetic sensor array and a predefined axis. The circuit mayadditionally include a distance sensor for determining a distance oftranslation of the magnetic sensor array with respect to a predefinedreference point. The circuit may also include a transmitter (e.g., awireless transmitter) for transmitting the relative position, thedetermined angle, and the determined distance to a controller such as acomputer of a CAOS system. The circuit may further include an indicator,such as a visual indicator, for informing a user of the apparatus thatthe magnetic sensor array is in a magnetic field of a magnetic source.

According to yet another aspect, a method for registering a bony anatomyof a patient with a CAOS system may include positioning a first magneticsensor array in a magnetic field of a first magnetic source coupled withthe bony anatomy of the patient and positioning a second magnetic sensorarray in a magnetic field of a second magnetic source coupled with thebony anatomy. Each of the magnetic sources may be embodied as one ormore magnets. The magnetic sensor arrays may be positioned by pivotingthe arrays about a common axis and/or moving the arrays along respectivelongitudinal axes. The method may also include determining firstposition data indicative of the position of the first magnetic sourcerelative to the first magnetic sensor array and second position dataindicative of the position of the second magnetic source relative to thesecond magnetic sensor array. Determining position data may includedetermining any one or more of the scalar components of thethree-dimensional magnetic flux density and/or determining the sixdegrees of freedom of the magnetic sources.

The method may also include determining position data indicative of theposition of a support frame coupled with the first and second magneticsensor arrays. The method may further include determining a firstdistance of translational of the first magnetic sensor array withrespect to a reference point and a second distance of translational ofthe second magnetic sensor array with respect to the reference point.Additionally, the method may include determining a first angle betweenthe first magnetic sensor array and a reference axis and a second anglebetween the second magnetic sensor array and the reference axis. Themethod may yet further include transmitting the first and secondposition data, the first and second distances, and the first and secondangles to a controller. Yet further, the method may include coupling themagnetic sources to the bony anatomy of the patient. Additionally, themethod may include retrieving an image of the bony anatomy from anelectronic file and creating a graphically rendered image of the bonyanatomy based on the image data, the position data, the determineddistance, and the determined angle.

The above and other features of the present disclosure, which alone orin any combination may comprise patentable subject matter, will becomeapparent from the following description and the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description particularly refers to the following figures,in which:

FIG. 1 is a perspective view of a computer assisted orthopaedic surgery(CAOS) system;

FIG. 2 is a simplified diagram of the CAOS system of FIG. 1;

FIG. 3 is a perspective view of a bone locator tool;

FIG. 4 is a perspective view of a registration tool for use with thesystem of FIG. 1;

FIG. 5 is a perspective view of an orthopaedic surgical tool for usewith the system of FIG. 1;

FIG. 6 is a simplified flowchart diagram of an algorithm that is used bythe CAOS system of FIG. 1;

FIG. 7 is a simplified flowchart diagram of one particular embodiment ofthe algorithm of FIG. 6;

FIGS. 8-17 illustrate various screen images that are displayed to asurgeon during the operation of the system of FIG. 1

FIG. 18 is a simplified diagram of another CAOS system including amagnetic sensor array;

FIG. 19 is a simplified circuit diagram of one embodiment of a sensorcircuit of the magnetic sensor array of FIG. 18;

FIG. 20 is a plan view of one embodiment of a magnetic sensorarrangement of the sensor circuit of FIG. 19;

FIG. 21 is a side elevation view of another embodiment of the magneticsensor array of FIG. 18;

FIG. 22 is a side elevation view of yet another embodiment of themagnetic sensor array of FIG. 18;

FIG. 23 is a perspective view of one embodiment of a magnetic source;

FIG. 24 is a simplified flowchart of an algorithm for registering a bonewith a CAOS system;

FIG. 25 is a simplified flowchart of an algorithm for generating athree-dimensional image of a bone;

FIG. 26 is a simplified flowchart of an algorithm for operating amagnetic sensor array;

FIG. 27 is a simplified flowchart of an algorithm for determining aposition of a magnetic source;

FIG. 28 is a simplified flowchart of an algorithm for determining aposition of a bony anatomy of a patient;

FIG. 29 is a simplified flowchart of an algorithm for determining atranslation and rotation matrix relating the positions of two or moremagnets;

FIG. 30 is a side elevation view of a test apparatus coupled to themagnetic sensor array of FIG. 18;

FIG. 31 is a perspective view of an implantable capsule for use with themagnetic source of FIG. 23;

FIG. 32 is a side cross-sectional view of the implantable capsule ofFIG. 31 implanted into a bone of a patient;

FIG. 33 is a perspective view of a jig assembly for implanting thecapsule of FIG. 31;

FIG. 34 is a side elevation view of another embodiment of a magneticsensor array;

FIG. 35 is a side elevation view of one embodiment of a magnetic sensorapparatus;

FIG. 36 is a simplified circuit diagram of one embodiment of a sensorcircuit of the magnetic sensor apparatus of FIG. 27;

FIG. 37 is a simplified flowchart of an algorithm for registering a bonewith a CAOS system using the magnetic sensor apparatus of FIG. 27; and

FIG. 38 is a simplified flowchart of a sub-algorithm of the algorithm ofFIG. 29.

DETAILED DESCRIPTION OF THE DRAWINGS

While the concepts of the present disclosure are susceptible to variousmodifications and alternative forms, specific exemplary embodimentsthereof have been shown by way of example in the drawings and willherein be described in detail. It should be understood, however, thatthere is no intent to limit the concepts of the present disclosure tothe particular forms disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

Referring to FIG. 1, a computer assisted orthopaedic surgery (CAOS)system 10 includes a computer 12 and a camera unit 14. The CAOS system10 may be embodied as any type of computer assisted orthopaedic surgerysystem. Illustratively, the CAOS system 10 is embodied as a Ci™ systemcommercially available from DePuy Orthopaedics, Inc. of Warsaw, Ind. Thecamera unit 14 may be embodied as a mobile camera unit 16 or a fixedcamera unit 18. In some embodiments, the system 10 may include bothtypes of camera units 16, 18. The mobile camera unit 16 includes a stand20 coupled with a base 22. The base 22 may include a number of wheels 21to allow the mobile camera unit 16 to be repositioned within a hospitalroom 23. The mobile camera unit 16 includes a camera head 24. The camerahead 24 includes two cameras 26. The camera head 24 may be positionablerelative to the stand 20 such that the field of view of the cameras 26may be adjusted. The fixed camera unit 18 is similar to the mobilecamera unit 16 and includes a base 28, a camera head 30, and an arm 32coupling the camera head 30 with the base 28. In some embodiments, otherperipherals, such as display screens, lights, and the like, may also becoupled with the base 28. The camera head 30 includes two cameras 34.The fixed camera unit 18 may be coupled to a ceiling, as illustrativelyshown in FIG. 1, or a wall of the hospital room. Similar to the camerahead 24 of the camera unit 16, the camera head 30 may be positionablerelative to the arm 32 such that the field of view of the cameras 34 maybe adjusted. The camera units 14, 16, 18 are communicatively coupledwith the computer 12. The computer 12 may be mounted on or otherwisecoupled with a cart 36 having a number of wheels 38 to allow thecomputer 12 to be positioned near the surgeon during the performance ofthe orthopaedic surgical procedure.

Referring now to FIG. 2, the computer 12 illustratively includes aprocessor 40 and a memory device 42. The processor 40 may be embodied asany type of processor including, for example, discrete processingcircuitry (e.g., a collection of logic devices), general purposeintegrated circuit(s), and/or application specific integrated circuit(s)(i.e., ASICs). The memory device 42 may be embodied as any type ofmemory device and may include one or more memory types, such as, randomaccess memory (i.e., RAM) and/or read-only memory (i.e., ROM). Inaddition, the computer 12 may include other devices and circuitrytypically found in a computer for performing the functions describedherein such as, for example, a hard drive, input/output circuitry, andthe like.

The computer 12 is communicatively coupled with a display device 44 viaa communication link 46. Although illustrated in FIG. 2 as separate fromthe computer 12, the display device 44 may form a portion of thecomputer 12 in some embodiments. Additionally, in some embodiments, thedisplay device 44 or an additional display device may be positioned awayfrom the computer 12. For example, the display device 44 may be coupledwith the ceiling or wall of the operating room wherein the orthopaedicsurgical procedure is to be performed. Additionally or alternatively,the display device 44 may be embodied as a virtual display such as aholographic display, a body mounted display such as a heads-up display,or the like. The computer 12 may also be coupled with a number of inputdevices such as a keyboard and/or a mouse for providing data input tothe computer 12. However, in the illustrative embodiment, the displaydevice 44 is a touch-screen display device capable of receiving inputsfrom an orthopaedic surgeon 50. That is, the surgeon 50 can provideinput data to the computer 12, such as making a selection from a numberof on-screen choices, by simply touching the screen of the displaydevice 44.

The computer 12 is also communicatively coupled with the camera unit 16(and/or 18) via a communication link 48. Illustratively, thecommunication link 48 is a wired communication link but, in someembodiments, may be embodied as a wireless communication link. Inembodiments wherein the communication link 48 is a wireless signal path,the camera unit 16 and the computer 12 include wireless transceiverssuch that the computer 12 and camera unit 16 can transmit and receivedata (e.g., image data). Although only the mobile camera unit 16 isshown in FIG. 2, it should be appreciated that the fixed camera unit 18may alternatively be used or may be used in addition to the mobilecamera unit 16.

The CAOS system 10 may also include a number of sensors or sensor arrays54 which may be coupled the relevant bones of a patient 56 and/or withorthopaedic surgical tools 58. For example, as illustrated in FIG. 3, atibial array 60 includes a sensor array 62 and bone clamp 64. Theillustrative bone clamp 64 is configured to be coupled with a tibia bone66 of the patient 56 using a Schantz pin 68, but other types of boneclamps may be used. The sensor array 62 is coupled with the bone clamp64 via an extension arm 70. The sensor array 62 includes a frame 72 andthree reflective elements or sensors 74. The reflective elements 74 areembodied as spheres in the illustrative embodiment, but may have othergeometric shapes in other embodiments. Additionally, in otherembodiments sensor arrays having more than three reflective elements maybe used. The reflective elements 74 are positioned in a predefinedconfiguration that allows the computer 12 to determine the identity ofthe tibial array 60 based on the configuration. That is, when the tibialarray 60 is positioned in a field of view 52 of the camera head 24, asshown in FIG. 2, the computer 12 is configured to determine the identityof the tibial array 60 based on the images received from the camera head24. Additionally, based on the relative position of the reflectiveelements 74, the computer 12 is configured to determine the location andorientation of the tibial array 60 and, accordingly, the tibia 66 towhich the array 60 is coupled.

Sensor arrays may also be coupled to other surgical tools. For example,a registration tool 80, as shown in FIG. 4, is used to register pointsof a bone as discussed in more detail below in regard to FIG. 7. Theregistration tool 80 includes a sensor array 82 having three reflectiveelements 84 coupled with a handle 86 of the tool 80. The registrationtool 80 also includes pointer end 88 that is used to register points ofa bone. The reflective elements 84 are also positioned in aconfiguration that allows the computer 12 to determine the identity ofthe registration tool 80 and its relative location (i.e., the locationof the pointer end 88). Additionally, sensor arrays may be used on othersurgical tools such as a tibial resection jig 90, as illustrated in FIG.5. The jig 90 includes a resection guide portion 92 that is coupled witha tibia bone 94 at a location of the bone 94 that is to be resected. Thejig 90 includes a sensor array 96 that is coupled with the portion 92via a frame 95. The sensor array 96 includes three reflective elements98 that are positioned in a configuration that allows the computer 12 todetermine the identity of the jig 90 and its relative location (e.g.,with respect to the tibia bone 94).

The CAOS system 10 may be used by the orthopaedic surgeon 50 to assistin any type of orthopaedic surgical procedure including, for example, atotal knee replacement procedure. To do so, the computer 12 and/or thedisplay device 44 are positioned within the view of the surgeon 50. Asdiscussed above, the computer 12 may be coupled with a movable cart 36to facilitate such positioning. The camera unit 16 (and/or camera unit18) is positioned such that the field of view 52 of the camera head 24covers the portion of a patient 56 upon which the orthopaedic surgicalprocedure is to be performed, as shown in FIG. 2.

During the performance of the orthopaedic surgical procedure, thecomputer 12 of the CAOS system 10 is programmed or otherwise configuredto display images of the individual surgical procedure steps which formthe orthopaedic surgical procedure being performed. The images may begraphically rendered images or graphically enhanced photographic images.For example, the images may include three dimensional rendered images ofthe relevant anatomical portions of a patient. The surgeon 50 mayinteract with the computer 12 to display the images of the varioussurgical steps in sequential order. In addition, the surgeon mayinteract with the computer 12 to view previously displayed images ofsurgical steps, selectively view images, instruct the computer 12 torender the anatomical result of a proposed surgical step or procedure,or perform other surgical related functions. For example, the surgeonmay view rendered images of the resulting bone structure of differentbone resection procedures. In this way, the CAOS system 10 provides asurgical “walk-through” for the surgeon 50 to follow while performingthe orthopaedic surgical procedure.

In some embodiments, the surgeon 50 may also interact with the computer12 to control various devices of the system 10. For example, the surgeon50 may interact with the system 10 to control user preferences orsettings of the display device 44. Further, the computer 12 may promptthe surgeon 50 for responses. For example, the computer 12 may promptthe surgeon to inquire if the surgeon has completed the current surgicalstep, if the surgeon would like to view other images, and the like.

The camera unit 16 and the computer 12 also cooperate to provide thesurgeon with navigational data during the orthopaedic surgicalprocedure. That is, the computer 12 determines and displays the locationof the relevant bones and the surgical tools 58 based on the data (e.g.,images) received from the camera head 24 via the communication link 48.To do so, the computer 12 compares the image data received from each ofthe cameras 26 and determines the location and orientation of the bonesand tools 58 based on the relative location and orientation of thesensor arrays 54, 62, 82, 96. The navigational data displayed to thesurgeon 50 is continually updated. In this way, the CAOS system 10provides visual feedback of the locations of relevant bones and surgicaltools for the surgeon 50 to monitor while performing the orthopaedicsurgical procedure.

Referring now to FIG. 6, an algorithm 100 for assisting a surgeon inperforming an orthopaedic surgical procedure is executed by the computer12. The algorithm 100 begins with a process step 102 in which the CAOSsystem 10 is initialized. During process step 102, settings,preferences, and calibrations of the CAOS system 10 are established andperformed. For example, the video settings of the display device 44 maybe selected, the language displayed by the computer 12 may be chosen,and the touch screen of the display device 44 may be calibrated inprocess step 102.

In process step 104, the selections and preferences of the orthopaedicsurgical procedure are chosen by the surgeon. Such selections mayinclude the type of orthopaedic surgical procedure that is to beperformed (e.g., a total knee arthroplasty), the type of orthopaedicimplant that will be used (e.g., make, model, size, fixation type,etc.), the sequence of operation (e.g., the tibia or the femur first),and the like. Once the orthopaedic surgical procedure has been set up inprocess step 104, the bones of the patient are registered in processstep 106. To do so, sensor arrays, such as the tibial array 60illustrated in FIG. 3, are coupled with the relevant bones of thepatient (i.e., the bones involved in the orthopaedic surgicalprocedure). Additionally, the contours of such bones are registeredusing the registration tool 80. To do so, the pointer end 88 of the tool80 is touched to various areas of the bones to be registered. Inresponse to the registration, the computer 12 displays rendered imagesof the bones wherein the location and orientation of the bones aredetermined based on the sensor arrays coupled therewith and the contoursof the bones are determined based on the registered points. Because onlya selection of the points of the bone is registered, the computer 12calculates and renders the remaining areas of the bones that are notregistered with the tool 80.

Once the pertinent bones have been registered in process step 106, thecomputer 12, in cooperation with the camera unit 16, 18, displays theimages of the surgical steps of the orthopaedic surgical procedure andassociated navigation data (e.g., location of surgical tools) in processstep 108. To do so, the process step 108 includes a number of sub-steps110 in which each surgical procedure step is displayed to the surgeon 50in sequential order along with the associated navigational data. Theparticular sub-steps 110 that are displayed to the surgeon 50 may dependon the selections made by the surgeon 50 in the process step 104. Forexample, if the surgeon 50 opted to perform a particular proceduretibia-first, the sub-steps 110 are presented to the surgeon 50 in atibia-first order

Referring now to FIG. 7, in one particular embodiment, an algorithm 120for assisting a surgeon in performing a total knee arthroplastyprocedure may be executed by the computer 12. The algorithm 120 includesa process step 122 in which the CAOS system 10 is initialized. Theprocess step 122 is similar to the process step 102 of the algorithm 100described above in regard to FIG. 6. In process step 122, thepreferences of the CAOS system 10 are selected and calibrations are set.To do so, the computer 12 displays a user initialization interface 160to the surgeon 50 via the display device 44 as illustrated in FIG. 8.The surgeon 50 may interact with the interface 160 to select variousinitialization options of the CAOS system 10. For example, the surgeon50 may select a network settings button 162 to change the networksettings of the system 10, a video settings button 164 to change thevideo settings of the system 10, a language button 166 to change thelanguage used by the system 10, and/or a calibration button 168 tochange the calibrations of the touch screen of the display device 44.The surgeon 50 may select a button by, for example, touching anappropriate area of the touch screen of the display device 44, operatingan input device such as a mouse to select the desired on-screen button,or the like.

Additional images and/or screen displays may be displayed to the surgeon50 during the initialization process. For example, if the surgeon 50selects the button 162, a network setting interface may be displayed onthe device 44 to allow the surgeon 50 to select different values,connections, or other options to change the network settings. Once theCAOS system 10 has been initialized, the surgeon 50 may close the userinitialization interface 160 by selecting a close button 170 and thealgorithm 120 advances to the process step 124.

In process step 124, selections of the orthopaedic surgical procedureare chosen by the surgeon 50. The process step 124 is similar to theprocess step 104 of the algorithm 100 described above in regard to FIG.6. For example, the selections made in the process step 104 may include,but are not limited to, the type of orthopaedic surgical procedure thatis to be performed, the type of orthopaedic implant that will be used,and the sequence of operation, and the like. To do so, a number ofprocedure preference selection screens may be displayed to the surgeon50 via the display device 44. For example, as illustrated in FIG. 9, anavigation order selection screen 180 may be displayed to the surgeon50. The surgeon 50 may interact with the screen 180 to select thenavigational (i.e., surgical) order of the orthopaedic surgicalprocedure being performed (i.e., a total knee arthroplasty procedure inthe illustrative embodiment). For example, the surgeon 50 may select abutton 182 to instruct the controller 12 that the tibia bone of thepatient 56 will be operated on first, a button 184 to instruct thecontroller 12 that the femur bone will be operated on first, or a button186 to select a standardized navigation order based on, for example, thetype of orthopaedic implant being used. The surgeon 50 may also navigateamong the selection screens by a back button 188 to review previouslydisplayed orthopaedic surgical procedure set-up screens or a next button190 to proceed to the next orthopaedic surgical procedure set-up screen.Once the surgeon 50 has selected the appropriate navigation order and/orother preferences and settings of the orthopaedic surgical procedurebeing performed, the algorithm 120 advances to the process step 126.

In the process step 126, the relevant bones of the patient 56 areregistered. The process step 126 is similar to the registration processstep 106 of the algorithm 100. The process step 126 includes a number ofsub-steps 128-136 in which the bones of the patient 56 involved in theorthopaedic surgical procedure are registered. In process step 128, therelevant bones are initially registered. That is, in the illustrativealgorithm 120, a tibia and a femur bone of the patient 56 are initiallyregistered. To do so, a tibia array, such as the tibia array 60illustrated in and described above in regard to FIG. 3, and a femurarray are coupled with the respective bones. The tibia and femur arraysare coupled in the manner described above in regard to the tibia array60. The camera head 24 of the camera unit 16 is adjusted such that thetibia and femur arrays are within the field of view 52 of the camerahead 24. Once the arrays are coupled and the camera head 24 properlypositioned, the tibia and femur of the patient 56 are initiallyregistered.

To do so, the controller 12 displays a user interface 200 to the surgeon50 via the display device 44, as shown in FIG. 10. The interface 200includes several navigation panes 202, 204, 206, a surgical step pane208, and a tool bar 210. Navigational data is displayed to the surgeon50 in the navigation panes 202, 204, 206. The computer 12 displaysdifferent views of the bone and/or surgical tools 58 in each of thepanes 202, 204, 206. For example, a frontal view of the patient's 56 hipand femur bone is displayed in the navigation pane 202, a sagittal viewof the patient's 56 bones is displayed in the navigation pane 204, andan oblique view of the patient's 56 bones is displayed in the navigationpane 206.

The computer 12 displays the surgical procedure steps in the pane 208.For example, in FIG. 10, the computer 12 is requesting the leg of thepatient 56 be moved about in a circular motion such that the femur boneof the patient 56 is initially registered. In response, the computer 12determines the base location and orientation of the femur bone (e.g.,the femur head) of the patient 56 based on the motion of the sensorarray 54 coupled with the bone (i.e., based on the image data of thesensor array 54 received from the camera head 24). Although only thefemur bone is illustrated in FIG. 10 as being initially registered, itshould be appreciated that the tibia bone is also initially registeredand that other images and display screen are displayed to the surgeon 50during such initial registration.

The surgeon 50 can attempt to initially register the bones as many timesas required by selecting a “try again” button 212. Once the relevantbones have been initially registered, the surgeon 50 can advance to thenext surgical procedure step of the registration step 126 by selectingthe next button 214. Alternatively, the surgeon 50 can skip one or moreof the initial registration steps by selecting the button 214 andadvancing to the next surgical procedure step while not performing theinitial registration step (e.g., by not initially registering the femurbone of the patient 56). The surgeon 50 may also go back to the previoussurgical procedure step (e.g., the initial registration of the tibia) byselecting a back button 216. In this way, the surgeon 50 can navigatethrough the surgical setup, registration, and procedure steps via thebuttons 214, 216.

The toolbar 210 includes a number of individual buttons, which may beselected by the surgeon 50 during the performance of the orthopaedicsurgical procedure. For example, the toolbar 210 includes an informationbutton 218 that may be selected to retrieve and display information onthe application software program being executed by the computer 12 suchas the version number, “hotline” phone numbers, and website links. Thetoolbar 210 also includes zoom buttons 220 and 222. The zoom button 220may be selected by the surgeon 50 to zoom in on the rendered imagesdisplayed in the panes 202, 204, 206 and the zoom button 222 may be usedto zoom out. A ligament balancing button 224 may be selected to proceedto a ligament balancing procedure, which is described in more detailbelow in regard to process step 152. A 3D model button 226 may beselected to alternate between the displaying of the rendered bone (e.g.,femur or tibia) and displaying only the registered points of therendered bone in the navigation panes 202, 204, and 206. An implantinformation button 228 may be selected to display information related toan orthopaedic implant selected during later steps of the orthopaedicsurgical procedure (e.g., process steps 140 and 146 described below).Such information may include, for example, the make, type, and size ofthe orthopaedic implant. A registration verification button 230 may beselected by the surgeon 50 at any time during the procedure to verifythe rendered graphical model of a bone if, for example, the sensorarrays 54 coupled with the bone are accidentally bumped or otherwisemoved from their fixed position. A screenshot button 232 may also beselected by the surgeon 50 at any time during the performance of theorthopaedic surgical procedure to record and store a screenshot of theimages displayed to the surgeon 50 at that time. The screenshots 50 maybe recorded in a storage device, such as a hard drive, of the computer12. A close button 234 may be selected to end the current navigation andsurgical procedure walk-through. After selecting the button 234, anyinformation related to the orthopaedic surgical procedure that has beenrecorded, such as screenshots and other data, are stored in the storagedevice of the computer 12 for later retrieval and review.

The toolbar 210 also includes a status display 236. The status display236 displays different color lights that indicate whether the system 10can “see” or otherwise detect the sensor arrays 54 coupled with thebones and/or surgical tools. The status display 236 is also a buttonthat may be selected to view a help screen illustrating a graphicalrendering of the field of view 52 of the camera head 24 such that thepositioning of the camera unit 16 and the sensor arrays 54 and surgicaltools 58 can be monitored and adjusted if needed.

Once the initial registration of the tibia and femur bones of thepatient 56 is complete, the algorithm 120 advances to process step 130in which the contour of the proximal tibia of the patient 56 isregistered. To do so, the surgeon 50 uses a registration tool, such asthe registration tool 80 illustrated in and described above in regard toFIG. 4. As illustrated in FIG. 11, the surgeon 50 registers the proximaltibia by placing the pointer end 88 of the registration tool 80 on thesurface of the tibia bone as instructed in the surgical step pane 208.Contour points of the tibia bone are recorded by the computer 12periodically as the pointer end 88 is dragged across the surface of thetibia bone and/or placed in contact with the tibia bone. The surgeon 50registers enough points on the proximal tibia such that the computer 12can determine and display a relatively accurate rendered model of therelevant portions of the tibia bone. Portions of the tibia bone that arenot registered, but rather rendered by the computer 12 based on apredetermined model of the tibia bone, are displayed to the surgeon 50in a different color than the registered portions of the tibia bone. Inthis way, the surgeon 50 can monitor the registration of the tibia boneand ensure that all relevant portions of the tibia bone have beenregistered to improve the accuracy of the displayed model.

Once all the relevant portions of the proximal tibia have beenregistered in process step 130, the tibia model is calculated andverified in process step 132. To do so, the surgeon 50 follows theinstructions provided in the surgical step pane 208. The proximal tibiais verified by touching the pointer end 88 of the registration tool 80to the registered portions of the tibia bone and monitoring the distancedata displayed in the pane 208 as illustrated in FIG. 12. Based on thedistance data, the surgeon 50 can determine if the current tibia modelis accurate enough for the orthopaedic surgical procedure. If not, thesurgeon 50 can redo the registration of the proximal tibia or supplementthe registration data with additional registration points by selectingthe back button 216. Once the model of the patient's 56 tibia has beendetermined to be sufficiently accurate, the surgeon 50 may proceed byselecting the next button 214.

The distal femur of the patient 56 is registered next in the processstep 134. The registration of the femur in process step 134 is similarto the registration of the tibia in the process step 130. That is, theregistration tool 80 is used to registered data points on the distalfemur. Once the registration of the femur is complete, the femur modelis calculated and verified in process step 136. The verification of thefemur in process step 136 is similar to the verification of the tibia inprocess step 132. The registration tool 80 may be used to touchpre-determined portions of the femur to determine the accuracy of thefemur model. Based on the distance data displayed in the surgical steppane 208, the surgeon 50 may reregister the femur or add additionregistration data points to the model by selecting the back button 216.Once the femur bone model is verified, the surgeon 50 can proceed withthe orthopaedic surgical procedure by selecting the next button 214.

Once the relevant bones (i.e., the proximal tibia and distal femur) havebeen registered in process step 126, the algorithm 120 advances toprocess step 138 in which the computer 12 displays images of theindividual surgical steps of the orthopaedic surgical procedure and theassociated navigation data to the surgeon 50. To do so, the process step138 includes a number of sub-steps 140-154. In process step 140 theplanning for the tibial implant is performed. Typically, the selectionof the tibial implant is performed in the process step 124, but may bemodified in the process step 140 depending upon how well the selectedimplant fits with the proximal tibia. As illustrated in FIG. 13, agraphically rendered model of the tibial implant is displayedsuperimposed over the rendered model of the tibia bone in the navigationpanes 202, 204, 206. The positioning of the tibial implant can beadjusted via the selection of a number of implant adjustment buttons.For example, the varus/valgus rotation of the orthopaedic implant may beadjusted via the buttons 240, the superior/inferior or proximal/distaltranslational of the orthopaedic implant may be adjusted via the buttons242, the slope of the orthopaedic implant may be adjusted via thebuttons 244, the anterior/posterior translational of the orthopaedicimplant may be adjust via the buttons 246, the internal/externalrotation of the orthopaedic implant may be adjusted by the buttons 248,and the medial/lateral translational of the orthopaedic implant may beadjusted by the buttons 250. Data related to the positioning of theorthopaedic implant is displayed in the surgical step panel 208. Someattributes of the implant, such as the orthopaedic implant size andthickness may be adjusted via the selection of button panels 252 and254, respectively. Additionally the original location and orientation ofthe implant may be reset via selection of a reset button 256. Using thevarious implant adjustment buttons and the implant attribute buttonpanels 252, 254, the surgeon 50 positions and orientates the tibialimplant such that a planned resection plane 258 of the tibia bone isdetermined. Because the surgeon 50 can see a visual rendering of theplanned resection plane and the location/orientation of the tibialimplant, the surgeon 50 can alter the location and orientation of theresection plane and/or tibial implant until the surgeon 50 is satisfiedwith the final fitting of the tibial implant to the resected proximaltibia. Once so satisfied, the surgeon 50 may proceed to the nextsurgical step by selecting the next button select the next button 214.

In process step 142 the resectioning of the proximal tibia is planned.To do so, a resection jig, such as the tibial resection jig 90illustrated in and described above in regard to FIG. 5, is coupled withthe tibia bone of the patient 56 near the desired resection location ofthe proximal tibia. As illustrated in FIG. 14, the computer 12 displaysthe correct surgical tool to use in the present step in the surgicalstep pane 208. In response, the computer 12 displays an actual resectionplane 260 to the surgeon 50 on the navigation panes 202, 204, 206. Asshown, a planned resection plane 258, as determined in step 140, is alsodisplayed. The surgeon 50 may then adjust the coupling of the jig 90with the tibia bone of the patient 56 such that the actual resectionplane 260 overlaps or nearly overlaps the planned resection plane 258.In this way, the surgeon 50 is able to visually monitor the actualresection plane 260 while adjusting the jig 90 such that an accurateresection of the tibia can occur. The surgeon 50 may advance to the nextsurgical step by selecting the next button 214.

Once the surgeon 50 has reviewed and adjusted the actual resection plane260 in process step 142, the algorithm 120 advances to process step 144.In process step 144, the tibia is resected using the appropriateresection tool and the jig 90 coupled with the tibia bone of the patient56. After the proximal tibia has been resected, the computer 12 displaysa verified resection plane 260 superimposed with the planned resectionplane 258 as illustrated in FIG. 15. The computer 12 also displays datarelated to the resection of the proximal tibia, including actual,planned, and deviation measurements, in the surgical step panel 208. Inthis way, the surgeon 50 can compare the final resection of the tibiaand the planned resection. If needed, the surgeon 50 can repeat theresectioning process to remove more the proximal tibia. Once the surgeon50 is satisfied with the resection of the tibia bone, the surgeon 50 mayadvance to the next surgical step by selecting the next button 214.

Once the tibia bone of the patient 56 has been resected, the relevantdistal femur bone is resected in process steps 146-150. In process step146, the planning for the femoral implant is performed. The femoralimplant planning of process step 146 is similar to the tibial implantplanning performed in process step 124. During process step 146, thesurgeon 50 positions and orients the femoral implant such that a plannedresection plane of the distal femur is determined and may also selectrelevant implant parameters (e.g., size, type, etc.). Because thesurgeon 50 can see a visual rendering of the planned resection plane andthe location/orientation of the femoral implant, the surgeon 50 canalter the location and orientation of the planned resection plane and/orfemoral implant until the surgeon 50 is satisfied with the final fittingof the femoral implant to the resected distal femur.

Once the femoral implant planning is complete, the algorithm 120advances to process step 148. In process step 148, the resectioning ofthe distal femur of the patient 56 is planned. The resection planning ofthe process step 148 is similar to the planning of the tibia resectionperformed in the process step 142. During the process step 148, afemoral resection jig is coupled with the femur bone of the patient 56.In response, the computer 12 displays an actual resection planesuperimposed on the planned resection plane developed in process step146. By repositioning the femoral resection jig, the surgeon 50 is ableto alter the actual resection plane such that an accurate resection ofthe femur can occur.

Once the surgeon 50 has reviewed and adjusted the actual resection planeof the femur bone, the algorithm 120 advances to process step 150 inwhich the distal femur is resected using the appropriate resection tooland femoral jig. After the distal femur has been resected, the computer12 displays a verified resection plane superimposed with the plannedresection plane determined in process step 146. In this way, the surgeon50 can compare the final resection of the femur with the plannedresection. Again, if needed, the surgeon 50 can repeat the resectioningprocess to remove more the distal femur.

Once the distal femur of the patient 56 has been resected, the algorithm120 advances to process step 152. In process step 152, ligamentbalancing of the patient's 56 tibia and femur is performed. Althoughillustrated as occurring after the resectioning of the tibia and femurbones in FIG. 7, ligament balancing may occur immediately following anyresection step (e.g. after the tibia bone is resected) in otherembodiments. In process step 152, orthopaedic implant trials (i.e.,temporary orthopaedic implants similar to the selected orthopaedicimplants) are inserted between the resected ends of the femur and tibiaof the patient 56. As illustrated in FIG. 16, the computer 12 displaysalignment data of the femur and tibia bone to the surgeon 50 via thedisplay device 44. Specifically, the computer 12 displays a frontal viewof the femur bone and tibia bone of the patient 56 in a frontal viewpane 262 and a lateral view of the femur and tibia bones in a lateralview pane 264. Each of the panes 262, 264 display alignment data of thefemur and tibia bones. Additional alignment data is displayed in thesurgical step pane 208. The alignment data may be stored (e.g., in adata storage device included in the computer 20) by selection of a storebutton 266. The alignment data may subsequently be retrieved andreviewed or used in another procedure at a later time.

Ligament balancing is performed to ensure a generally rectangular shapedextension gap and a generally rectangular shaped flexion gap at apredetermined joint force value has been established between thepatient's 56 proximal tibia and the distal femur. To do so, a ligamentbalancer may be used to measure the medial and lateral joint forces andthe medial and lateral gap distances when the patient's 56 leg is inextension (i.e., the patient's 56 tibia is positioned at about 0 degreesrelative to the patient's femur) and in flexion (i.e., the patient's 56tibia is positioned at about 90 degrees relative to the patient'sfemur). An exemplary ligament balancer that may be used to perform thesemeasurements is described in U.S. patent application Ser. No.11/094,956, filed on Mar. 31, 2005, the entirety of which is expresslyincorporated herein by reference. In either extension or flexion, if themedial and lateral gap distances are not approximately equal (i.e., donot form a generally rectangular shaped joint gap) at the predeterminedjoint force value, ligament release (i.e., cutting of a ligament) may beperformed to equalize the medial and/or lateral gap distances.Additionally or alternatively, the orthopaedic implant trial may bereplaced with an alternative implant trial. In this way, the surgeon 50ensures an accurate alignment of the tibia bone and femur bone of thepatient 56.

Once any desired ligament balancing is completed in process step 152,the algorithm 120 advances to process step 154 in which a finalverification of the orthopaedic implants is performed. In process step154, the orthopaedic implants are coupled with the distal femur andproximal tibia of the patient 56 and the alignment of the femur andtibia bones are verified in flexion and extension. To do so, thecomputer 12 displays the rendered images of the femur bone and tibiabone and alignment data to the surgeon 50 via the display device 44, asillustrated in FIG. 17. As indicated in the surgical step pane 208, thesurgeon 50 is instructed to move the patient's 56 leg to flexion andextension such that the overall alignment can be determined andreviewed. If the femur and tibia bones of the patient 56 are notaligning (i.e., the flexion and/or extension gap is non-rectangular) tothe satisfaction of the surgeon 50, the surgeon may perform additionalligament balancing as discussed above in regard to process step 152.Once the surgeon 50 has verified the final alignment of the femur andtibia bones (i.e., the flexion and extension gaps), the surgeon 50 maystore the final alignment data via selecting the store button 266. Thesurgeon 50 may subsequently complete the orthopaedic surgical procedureby selecting the next button 214.

Referring now to FIG. 18, in another embodiment, a system 300 forpre-operatively registering a bone or bony anatomy (i.e., one or morebones) of a patient includes a computer assisted orthopaedic surgery(CAOS) system 301, a magnetic sensor array 308, and one or more magneticsources 309. The computer assisted orthopaedic surgery (CAOS) system 301includes a controller 302, a camera unit 304, and a display device 306.The controller 302 is communicatively coupled with the camera unit 304via a communication link 310. The communication link 310 may be any typeof communication link capable of transmitting data (i.e., image data)from the camera unit 304 to the controller 302. For example, thecommunication link 310 may be a wired or wireless communication link anduse any suitable communication technology and/or protocol to transmitthe image data. In the illustrative embodiment, the camera unit 304 issimilar to and operates in a similar manner as the camera unit 16 of thesystem 10 described above in regard to FIG. 1. For example, the cameraunit 304 includes a number of cameras (not shown) and may be used incooperation with the controller 302 to determine the location andorientation of a number of sensor arrays positioned in the field of viewof the camera unit 304, as discussed in detail above in regard to thecamera unit 16. The sensor arrays may include a number of reflectiveelements and may be coupled with bones of a patient and/or variousmedical devices, such as probes, saw guides, ligament balancers, and thelike, used during the orthopaedic surgical procedure. Alternatively, insome embodiments, the camera unit 304 may be replaced or supplementedwith a wireless receiver (which may be included in the controller 302 insome embodiments) and the sensor arrays may be embodied as wirelesstransmitters (e.g., electromagnetic transmitters). Additionally, themedical devices may be embodied as “smart” medical devices such as, forexample, smart surgical instruments, smart surgical trials, smartsurgical implants, and the like. In such embodiments, the controller 302is configured to determine the location of the medical devices based onwireless data signals received from the smart medical devices.

The controller 302 is communicatively coupled with the display device306 via a communication link 312. Although illustrated in FIG. 18 asseparate from the controller 302, the display device 306 may form aportion of the controller 302 in some embodiments. Additionally, in someembodiments, the display device 306 may be positioned away from thecontroller 302. For example, the display device 306 may be coupled witha ceiling or wall of the operating room wherein the orthopaedic surgicalprocedure is to be performed. Additionally or alternatively, the displaydevice 306 may be embodied as a virtual display such as a holographicdisplay, a body mounted display such as a heads-up display, or the like.The controller 302 may also be coupled with a number of input devicessuch as a keyboard and/or a mouse. However, in the illustrativeembodiment, the display device 302 is a touch-screen display devicecapable of receiving inputs from a surgeon using the CAOS system 301.That is, the surgeon can provide input data to the display device 306and controller 302, such as making a selection from a number ofon-screen choices, by simply touching the screen of the display device306.

The controller 302 may be embodied as any type of controller including,but not limited to, a computer such as a personal computer, aspecialized microcontroller device, a collection of processing circuits,or the like. The controller 302 includes a processor 314 and a memorydevice 316. The processor 314 may be embodied as any type of processorincluding, but not limited to, discrete processing circuitry and/orintegrated circuitry such as a microprocessor, a microcontroller, and/oror an application specific integrated circuit (ASIC). The memory device316 may include any number of memory devices and any type of memory suchas random access memory (RAM) and/or read-only memory (ROM). Althoughnot shown in FIG. 18, the controller 302 may also include othercircuitry commonly found in a computer system.

The controller 302 may also include a database 318. The database 318 maybe embodied as any type of database, electronic library, and/or filestorage location. For example, the database 318 may be embodied as astructured database or as an electronic file folder or directorycontaining a number of separate files and an associated “look-up” table.Further, the database 318 may be stored on any suitable device. Forexample, the database 318 may be stored in a set of memory locations of,for example, the memory device 316 and/or a stored on a separate storagedevice such as a hard drive or the like.

Additionally or alternatively, the controller 302 may be coupled to aremote database 320 via a communication link 322. The remote database320 may be similar to the database 318 and may be embodied as any typeof database, electronic library, and/or a file storage location. Theremote database 320 may be located apart from the controller 302. Forexample, the controller 302 may be located in an orthopaedic surgeryroom while the remote database 318 may form a part of a hospital networkand be located in a separate room or building apart from the orthopaedicsurgery room. As such, the communication link 322 may be embodied as anytype of communication link capable of facilitating data transfer betweenthe controller 302 and the remote database 320. For example, in someembodiments, the communication link 322 may form a portion of a networksuch as a Local Area Network (LAN), a Wide Area Network (WAN), and/or aglobal, publicly-accessible network such as the Internet. In use, thedatabase(s) 318, 320 is accessed by the controller 302 to store and/orretrieve images of a bone(s) of a patient as discussed in more detail inregard to FIG. 21.

The controller 302 also includes a receiver or transceiver 324. Thereceiver 324 is used by the processor 314 to communicate with themagnetic sensor array 308 via a communication link 326. Thecommunication link 326 may be embodied as any type of communication linkcapable of transmitting data from the magnetic sensor array 308 to thecontroller 302. For example, the communication link 326 may be a wiredor wireless communication link and use any suitable communicationtechnology and/or protocol to transmit the data. As such, the receiver324 may be embodied as any type of receiver capable of facilitatingcommunication between the controller 302 and the magnetic sensor array308 including, for example, a wired or wireless receiver.

The illustrative magnetic sensor array 308 of FIG. 18 includes a housing330 having a sensing head portion 332 and a handle 334 coupled to thehead portion 332. The handle 334 may be used by a user of the system300, such as an orthopaedic surgeon, to move and position the magneticsensor array 308. The magnetic sensor array 308 also includes a sensorcircuit 328 located in the head portion 332. As discussed in more detailbelow in regard to FIGS. 19-33, the sensor circuit 328 is configured tosense a magnetic field generated by the magnetic source 309 anddetermine data indicative of a position of the magnetic source 309relative to the magnetic sensor array 308 and transmit such data via thecommunication link 326 and receiver 324 to the controller 302. It shouldbe understood that, as used herein, the term “position” is intended torefer to any one or more of the six degrees of freedom which define thelocation and orientation of a body (e.g., the magnetic source 309) inspace or relative to a predetermined point or other body.

In some embodiments, the magnetic sensor array 308 may also include areflective sensor array 336. The reflective sensor array 336 includes asupport frame 338 and a number of reflective sensor elements 340. Thereflective sensor array 336 is similar to the sensor arrays 54, 62, 82,96 described above in regard to FIGS. 2, 3, 4, and 5, respectively. Thereflective sensor elements 340 are positioned in a predefinedconfiguration that allows the controller 302 to determine the identityand position (i.e., three dimensional location and orientation) of themagnetic sensor array 308 based on the configuration. That is, when themagnetic sensor array 308 is positioned in the field of view of thecamera unit 304, the controller 302 is configured to determine theidentity and position of the magnetic sensor array 308 relative to thecamera 304 and/or controller 302 based on the images received from thecamera unit 304 via the communication link 310. In other embodiments,the reflective sensor array 336 may replaced or complimented with awireless transmitter. In such embodiments, the controller 302 includes awireless receiver and is configured to determine the position andidentity of the magnetic sensor array based on transmitted data receivedfrom the wireless transmitter.

To sense the magnetic field(s) of the magnetic source 309, the sensorcircuit 328 includes a magnetic sensor arrangement 348 as illustrated inFIG. 19. The magnetic sensor arrangement 348 includes one or moremagnetic sensors 350. The sensor circuit 328 also includes a processingcircuit 352 and a transmitter 354. The magnetic sensors 350 areelectrically coupled to the processing circuit 352 via a number ofinterconnects 356. The processing circuit 352 is also electricallycoupled to the transmitter 354 via an interconnect 358. Theinterconnects 356, 358 may be embodied as any type of interconnectscapable of providing electrical connection between the processingcircuit 352, the sensors 350, and the transmitter 354 such as, forexample, wires, cables, PCB traces, or the like.

The number of magnetic sensors 350 that form the magnetic sensorarrangement 348 may depend on such criteria as the type of magneticsensors used, the specific application, and/or the configuration of themagnetic sensor array 308. For example, the magnetic sensors 350 areconfigured to measure a three-dimensional magnetic field of the magneticsource 309. As such, the sensor circuit 328 may include any number andconfiguration of one-dimensional, two-dimensional, and/orthree-dimensional magnetic sensors such that the sensor circuit 328 iscapable of sensing or measuring the magnetic field of the magneticsource 309 in three dimensions. Additionally, the magnetic sensor(s) 350may be embodied as any type of magnetic sensor capable of sensing ormeasuring the magnetic field generated by the magnetic source 309. Forexample, the magnetic sensors 350 may be embodied as superconductingquantum interference (SQUID) magnetic sensors, anisotropicmagnetoresistive (AMR) magnetic sensors, giant magnetoresistive (GMR)magnetic sensors, Hall-effect magnetic sensors, or any other type ofmagnetic sensors capable of sensing or measuring the three-dimensionalmagnetic field of the magnetic source. In one particular embodiment, themagnetic sensor(s) are embodied as X-H3X-xx_E3C-25HX-2.5-0.2T Three AxisMagnetic Field Transducers, which are commercially available from SENISGmbH, of Zurich, Switzerland. Regardless, the magnetic sensors 350 areconfigured to produce a number of data values (e.g., voltage levels)which define one or more of the components (e.g., X-, Y-, andZ-components) of the three-dimensional magnetic flux density of themagnetic field of the magnetic source 309 at the point in space whereeach sensor is located and in the orientation of each sensor's activesensing element. These data values are transmitted to the processingcircuit 352 via the interconnects 356.

In one particular embodiment, the magnetic sensor arrangement 348includes seventeen magnetic sensors 350 ₁-350 ₁₇ configured asillustrated in FIG. 20. The magnetic sensors 350 ₁-350 ₁₇ are secured toa sensor board 370. The sensor board 370 may be formed from anynon-magnetic material capable of supporting the magnetic sensors 350₁-350 ₁₇ in the desired configuration. For example, in the illustrativeembodiment, the sensor board 370 is formed from FR4. The magneticsensors 350 ₁-350 ₁₇ may be mounted on or in the sensor board 370. Assuch, the sensor board 370 forms the sensing face of the sensor circuit328 and may be located inside the head portion 332 of the magneticsensor array 308 (i.e., located behind the housing material) or mountedto the head portion 332 such that the sensor board 370 is exposed.

The illustrative sensor board 370 has a width 372 of about 5.8centimeters, a length 374 of about 5.8 centimeters, and a thickness (notshown) of about 1.25 centimeters. However, sensor boards having otherdimensions that allow the mounting of the desired number of magneticsensors 350 may be used. The magnetic sensors 350 are mounted to or inthe sensor board 370 according to a predetermined configuration. Forclarity of description, a grid 375 having an X-axis 376 and a Y-axis 378is illustrated over the sensor board 370 in FIG. 20. In the illustrativeembodiment, each unit of the grid 375 has a measurement of about 5millimeters. Each of the magnetic sensors 350 ₁-350 ₁₇ may be a onedimensional, two dimensional, or three dimensional sensor. As such, eachof the magnetic sensors 350 ₁-350 ₁₇ may include one, two, or threeactive sensing elements, respectively. Each sensing element of themagnetic sensors 350 ₁-350 ₁₇ is capable of measuring at least onecomponent of the magnetic flux density of a magnetic source at theposition (i.e., location and orientation) of the particular magneticsensor. To do so, each magnetic sensor 350 includes a field sensitivepoint, denoted as a “+” in FIG. 20, wherein the magnetic flux density ismeasured. The configuration of the magnetic sensors 350 ₁-350 ₁₇ will bedescribed below in reference to the field sensitive point of eachmagnetic sensor with the understanding that the body of the sensor maybe positioned in numerous orientations wherein each orientationfacilitates the same location of the field sensitive point.

As illustrated in FIG. 20, the first magnetic sensor 350 ₁ is located ata central point (0, 0) on the grid 375. The first magnetic sensor 350 ₁is a three-dimensional magnetic sensor having three channels andgenerates data values (i.e., voltage levels) indicative of the X-, Y-,and Z-components of the measured magnetic flux density at the positionof the sensor 350 ₁. Four additional three-dimensional magnetic sensors350 ₂-350 ₅ are positioned around the first magnetic sensor 350 ₁. Themagnetic sensor 350 ₂ is located at point (−15, 15), the magnetic sensor350 ₃ is located at point (−15, 15), the magnetic sensor 350 ₄ islocated at point (15, 15), and the magnetic sensor 350 ₅ is located atpoint (15, −15), wherein each graduation mark of the grid 375 is definedas 5 units (e.g., 5 millimeters).

The magnetic sensor arrangement 348 also includes a number ofsingle-dimensional magnetic sensors 350 ₆-350 ₁₇. The magnetic sensors350 ₆-350 ₁₃ are positioned on the sensor board 370 such that thesensors 350 ₆-350 ₁₃ measure the Z-component of the measured magneticflux density (i.e., the magnetic flux generated by the magnetic source309). In particular, the magnetic sensor 350 ₆ is located at point (0,−25), the magnetic sensor 350 ₇ is located at point (−25, 0), themagnetic sensor 350 ₈ is located at point (0, 25), the magnetic sensor350 ₉ is located at point (25, 0), the magnetic sensor 350 ₁₀ is locatedat point (−30, −30), the magnetic sensor 350 ₁₁ is located at point(−30, 30), the magnetic sensor 350 ₁₂ is located at point (30, 30), andthe magnetic sensor 350 ₁₃ is located at point (30, −30).

Conversely, the one-dimensional magnetic sensors 350 ₁₄, 350 ₁₆, and themagnetic sensors 350 ₁₅, 350 ₁₇ are positioned on the sensor board 370such that the one-dimensional sensors 350 ₁₄, 350 ₁₆ and 350 ₁₅, 350 ₁₇measure the magnitude of the Y-axis and X-axis components of themagnetic flux density of the measured magnetic field, respectively. Inparticular, the magnetic sensor 350 ₁₄ is located at point (0, −45), themagnetic sensor 350 ₁₅ is located at point (−45, 0), the magnetic sensor350 ₁₆ is located at point (0, 45), and the magnetic sensor 350 ₁₇ islocated at point (45, 0). As illustrated in FIG. 20, the magneticsensors 350 ₁₄-350 ₁₇ are positioned in or embedded in the sensor board370 such that the magnetic sensors 350 ₁₄-350 ₁₇ are positionedorthogonally to the measurement surface of the sensor board 370.Conversely, the magnetic sensors 350 ₁-350 ₁₃ are positioned on thesensor board 370 coplanar with the measurement surface of the sensorboard 370 or otherwise substantially parallel therewith.

In some embodiments, the magnetic sensors 350 may have differingmagnetic field sensitivities (i.e., the ability to detect a change inthe measured magnetic flux density) and sensing ranges. For example, insome embodiments, the magnetic sensors 350 located toward a centrallocation of the sensor board 370 may have a lower magnetic fieldsensitivity but a greater sensing range than the magnetic sensors 350located farther from the central location. In the illustrativeembodiment of FIG. 20, the three-dimensional magnetic sensors 350 ₁-350₅, which are located toward the center of the sensor board 370, have alower magnetic field sensitivity and a greater sensing range than theone-dimensional magnetic sensors 350 ₆-350 ₁₇ For example, in oneparticular embodiment, the three-dimensional magnetic sensors 350 ₁-350₅ have a magnetic sensitivity of about 50 μT (micro-Tesla) and a sensingrange of about 20 mT (milli-Tesla) while the one-dimensional magneticsensors 350 ₆-350 ₁₇ have a magnetic sensitivity of about 5 μT and asensing range of about 2 mT. However, in other embodiments, there may beadditional levels or differences of magnetic sensitivity and/or sensingrange based on the particular distance of each magnetic source 350 froma predetermined location on the sensor board 370.

Because of such differences in magnetic field sensitivity and sensingrange of the magnetic field sensors 350, the magnetic sensor arrangement348 may be less susceptible to positioning variances of the magneticsensor array 308 and/or the accuracy of the magnetic flux densitymeasurements may be improved by having magnetic sensors 350 capable ofmeasuring the magnetic flux density of the magnetic source 309 while themagnetic sensor array is positioned close to the magnetic source 309without going into saturation. Additionally, the magnetic sensorarrangement 348 may be less susceptible to positioning variances of themagnetic sensor array 308 and/or the accuracy of the magnetic fluxdensity measurements may be improved by having magnetic sensors 350capable of measuring the magnetic field of the magnetic source 309 whilethe magnetic sensor array 308 is positioned far from the magnetic source309 in spite of the increase in magnetic “noise” (i.e., undesirablemagnetic field effects from sources other than the magnetic source 309).To further improve the measurement accuracy of the magnetic sensor array308, the measurements of the array 308 may be verified as discussed indetail below in regard to process step 402 of algorithm 400 shown inFIG. 24.

It should be appreciated that the magnetic sensor arrangement 348 isonly one illustrative embodiment and that, in other embodiments, thesensor arrangement 348 of the sensor circuit 328 may include any numberof magnetic sensors 350 positioned in any configuration that allows themagnetic sensors 350 to measure the three-dimensional X-, Y-, andZ-components of the measured magnetic flux density. For example, in someembodiments, the magnetic sensor arrangement 348 may include a singlethree-dimensional magnetic sensor. Alternatively, in other embodiments,the magnetic sensor arrangement 348 may include additional magneticsensors 350 arranged in various configurations. It should be appreciatedthat by increasing the number of magnetic sensors, an amount ofredundancy is developed. That is, magnitudes of the individualcomponents of the measured magnetic flux densities are determined usingmeasurements from a number of magnetic sensors 350 positioned indifferent locations. For example, referring to the illustrative magneticsensor arrangement 348 illustrated in FIG. 20, the magnitudes of theZ-component of the measured magnetic flux densities are determined usingthe measurements from magnetic sensors 350 ₁-350 ₁₃. As such, it shouldbe appreciated that the accuracy of the characterization of thethree-dimensional magnetic field generated by the magnetic source 309may be increased by including additional magnetic sensors in themagnetic sensor arrangement 348.

Further, although the magnetic sensors 350 are embodied as separatemagnetic sensors apart from the processing circuit 352 in theillustrative embodiment of FIGS. 18-20, in some embodiments, themagnetic sensors 350 and the processing circuit 352, or portionsthereof, may be embodied as a single electronic device. For example, themagnetic sensors 350 and portions of the processing circuit 352 may beembodied as one or more complimentary metal oxide semiconductor (CMOS)device(s). By embedding the magnetic sensors 350 and processing circuit352 in a semiconductor device, the required space of the sensor circuit328 is reduced. Additionally, such a semiconductor device may be lesssusceptible to outside influences such as temperature variation of theindividual magnetic sensors 350.

Referring back to FIG. 19, the processing circuit 352 may be embodied asany collection of electrical devices and circuits configured todetermine the position of the magnetic source 309. For example, theprocessing circuit 352 may include any number of processors,microcontrollers, digital signal processors, and/or other electronicdevices and circuits. In addition, the processing circuit 352 mayinclude one or more memory devices for storing software/firmware code,data values, and algorithms.

In some embodiments, the processing circuit 352 is configured todetermine position data indicative of the position of the magneticsource 309 relative to the magnetic sensor array 308 based on themeasurements of magnetic sensors 350. To do so, the processing circuit352 may execute an algorithm for determining the position of themagnetic source 309 relative to the magnetic sensor array 308 asdiscussed in detail below in regard to algorithms 820 and 830 andillustrated in FIGS. 26 and 27. The position data may be embodied ascoefficient values or other data usable by the controller 302, alongwith pre-operative images of the relevant bones and magnetic sources309, to determine the position (i.e., location and orientation) of themagnetic source 309. The processing circuit 352 controls the transmitter354 via interconnect 358 to transmit the position data to the controller302 via the communication link 326. Alternatively, in other embodiments,the processing circuit 332 is configured only to transmit themeasurements of the magnetic sensors 350 to the controller 302 via thetransmitter 354. In response, the controller 302 executes the algorithmfor determining the position of the magnetic source 309 using themeasurements received from the magnetic sensor array 308. In suchembodiments, the overall footprint (i.e., size) of the sensor circuit328 may be reduced because some of the circuitry of the processingcircuit 352 may not be required since the processing circuit 352 is notconfigured to determine the position data.

In some embodiments, the sensor circuit 328 may also include anindicator 360. The indicator 360 may be embodied as any type ofindicator including a visual indicator, an audible indicator, and/or atactile indicator. The indicator 360 is electrically coupled to theprocessing circuit 352 via an interconnect 362, which may be similar tointerconnects 356, 358. In such embodiments, the processing circuit 352is configured to activate the indicator 360 when the magnetic sensorarray 308 (i.e., the magnetic sensors 350) is positioned in a magneticfield of a magnetic source 309. For example, the processing circuit 352may be configured to monitor the magnetic flux densities sensed by themagnetic sensor(s) 350 in one or more of the X-, Y-, and/or Z-directionsshown in FIG. 20 and activate the indicator 360 when the magnetic fluxdensity in one or more of the X-, Y-, and/or Z-directions reaches orsurpasses a predetermined threshold value. In this way, the magneticsensor array 308 is capable of notifying the surgeon or other user ofthe array 308 when the array 308 has been properly positioned such thatthe magnetic sensor array 308 can accurately sense or measure themagnetic flux density of the magnetic source 309.

Further, in some embodiments the sensor circuit 328 may include aregister button 364. The register button 364 may be located on anoutside surface of the magnetic sensor array 308 such that the button364 is selectable by a user (e.g., an orthopaedic surgeon) of the array308. The button 364 may be embodied as any type of button such as a pushbutton, toggle switch, software implemented touch screen button, or thelike. The register button 364 is electrically coupled to the processingcircuit 352 via an interconnect 366, which may be similar tointerconnects 356, 358. The register button 364 may be selected by auser, such as an orthopaedic surgeon, of the magnetic sensor array 308to transmit the position data and/or measurement values of the magneticsensors 350 to the controller 302. That is, as discussed in more detailbelow in regard to algorithm 820, once the magnetic sensor array isproperly positioned to measure the magnetic field of the magnetic source309, the surgeon may select the register button 364 to cause themagnetic sensor array to transmit the data. In some embodiments, theregister button 364 is only operable while the magnetic sensor array 308is properly positioned. For example, the register button 364 may beselected to transmit the position data/measured values only while theprocessing circuit 352 has determined that the measured magnetic fluxdensity (e.g., in the Z-axis direction) is above a predeterminedthreshold value or within a predetermined range of values. As discussedabove in regard to the indicator 360, the surgeon is notified when themagnetic sensor array is properly positioned by the activation of theindicator 360.

Although the illustrative magnetic sensor array 308 is illustrated as ahand-held device including the sensor circuit 328 located therein, inother embodiments, the magnetic sensor array 308 may be embodied as asingle magnetic sensor, a number of magnetic sensors, or a collection ofmagnetic sensors and other circuitry. Additionally, in otherembodiments, the magnetic sensor array 308 may include one or moreremote magnetic sensors located apart from the sensor circuit 328. Bydisplacing the remote magnetic sensor(s) from the sensor circuit 328,unwanted magnetic interferences caused by environmental magnetic fieldssuch as magnetic effects caused from the Earth's magnetic field, straymagnetic fields in the operating room, and the like, may be adjusted outof or otherwise compensated for in the sensor circuit 328 as discussedin more detail below in regard to process step 831 of algorithm 830described below in regard to and illustrated in FIG. 27.

As illustrated in FIG. 21, in some embodiments, the magnetic sensorarray 308 may include a remote magnetic sensor housing 380. The remotemagnetic sensor housing 380 includes a support frame 382 extending adistance 383 up from the head portion 332 of the magnetic sensor array308. The remote magnetic sensor housing 380 includes a head portion 384coupled to the top of the support frame 382. A remote magnetic sensor386 is located in the head portion 382 and electrically coupled to thesensor circuit 328 via an interconnect 388. The interconnect 388 may beany type of interconnect capable of providing communication between theremote magnetic sensor 386 and the sensor circuit 328. In someembodiments, the remote magnetic sensor housing 380 is capable of beingmechanically decoupled from the magnetic sensor array 308 such that thehousing 380 and remote magnetic sensor 386 may be positioned furtheraway from or in an alternative position in relation to the sensorcircuit 328.

The remote magnetic sensor 386 is similar to the magnetic sensors 350and may be a one-, two-, or three-dimensional magnetic sensor. In oneparticular embodiment, the remote magnetic sensor 386 is athree-dimensional sensor configured to measure the X-, Y-, andZ-components of the magnetic field at the position of the remotemagnetic sensor 386. The remote magnetic sensor 386 is spaced apart fromthe sensor circuit 328 such that interfering magnetic fields (i.e.,magnetic fields other than the desired magnetic field) may be measured.That is, the remote magnetic sensor 386 is located such that it is farenough away from the magnetic source 309 such that the magnetic fieldgenerated by the magnetic source 309 has minimal impact on themeasurements of the remote magnetic sensor 386. As such, the remotemagnetic sensor 386 is configured to measure magnetic fields generatedby sources other than the magnetic source 309. The measurementsgenerated by the remote magnetic sensor 386 are transmitted to thesensor circuit 328 via the interconnect 388. The sensor circuit 328 maybe configured to compensate or adjust the magnetic field measurements ofthe magnetic sensors 350 based on the measurements of the remotemagnetic sensor 386. In this way, unwanted magnetic field effects can besubtracted out of the measurements of the magnetic sensors 350 orotherwise accounted for.

Additionally, other embodiments of the magnetic sensor array 308 mayinclude a housing having different configurations than that illustratedin FIG. 18. For example, as illustrated in FIG. 22, a magnetic sensorarray 390 may include a sensing head portion 392 having the sensorcircuit 328 located therein. A handle 394 is coupled to the head portion392 and includes the remote magnetic sensor 386, which is electricallycoupled to the sensor circuit 328 via an interconnect 396. Theinterconnect 396 is similar to the interconnect 388 and may be embodiedas any type of interconnect capable of providing communication betweenthe remote magnetic sensor 386 and the sensor circuit 328. In theillustrative embodiments, the handle 394 is a closed loop handle and iscoupled to the sensing head portion 392 at each distal end. As discussedabove in regard to FIG. 21, the sensor circuit 328 uses the measurementsgenerated by the remote magnetic sensor 386 to compensate or calibratethe magnetic sensors 350 of the sensor circuit 328.

Referring now to FIG. 23, the magnetic source 309 may be embodied as oneor more magnets. In the illustrative embodiment, the magnetic source 309is embodied as two or more cylindrical, dipole magnets 450. Themagnet(s) 450 generate a magnetic field having a number a magnetic fluxlines 452. It should be appreciated that only a subset cross-section ofthe generated flux lines 452 is illustrated in FIG. 23 and that the fluxlines (and magnetic field) circumferentially surround the magnet(s) 450.When coupled to a bone(s) of a patient, the position (i.e., location andorientation) of the magnets 450 is defined by six degrees of freedom.That is, the position of the magnet(s) 450 can be defined by threeCartesian coordinate values and three rotational values (i.e., one abouteach Cartesian axis). For example, as illustrated in FIG. 23 bycoordinate axes 454, the position of the magnet(s) 450 can be defined inthree-dimensional space by an X-coordinate value, a Y-coordinate value,a Z-coordinate value, a (theta) θ-rotational value about the X axis, a(phi) φ-rotational value about the Y axis, and a (psi) ψ-rotationalvalue about the Z axis.

The magnet 450 may be formed from any magnetic material capable ofgenerating a magnetic field of sufficient magnetic flux density orstrength to be sensed or measured by the sensor circuit 328 through therelevant tissue of a patient. For example, the magnet 450 may be formedfrom ferromagnetic, ferrimagnetic, antiferromagnetic, antiferrimagnetic,paramagnetic, or superparamagnetic material. In one particularembodiment, the magnet 450 is formed from a neodymium ferrite boron(NdFeB) grade 50 alloy material. The illustrative magnet 450 is acylindrical magnet having a length 451 of about five millimeters and adiameter 453 of about two millimeters. However, in other embodiments,magnets 450 having other configurations, such as rectangular andspherical magnets, and sizes may be used.

To improve the accuracy of the measurements of the magnetic sensors 350,in some embodiments, the plurality of magnets 450 which embody themagnetic source 309 are formed or manufactured such that the magneticqualities of each magnet 450 are similar. To do so, in one embodiment,the magnetic field generated by each magnet 450 is measured anddetermined. Only those magnets 450 having similar magnetic fields areused. Additionally, in some embodiments, the magnetic moment of eachmagnet 450 may be determined. Only those magnets 450 with magneticmoments on-axis or near on-axis with the magnet's 450 longitudinal axisare used. That is, if the magnetic moment of the magnet 450 isdetermined to extend from the magnet 450 from a location substantiallyoff the longitudinal axis of the magnet 450, the magnet 450 may bediscarded. In this way, the magnetic fields generated by each of themagnets 450 are similar and, as such, measurements of the magneticfields and calculated values based thereon may have increased accuracy.

Referring now to FIGS. 24-29, an algorithm 400 for registering a bone ofa patient with a computer assisted orthopaedic surgery (CAOS) systembegins with an optional process step 402 in which the accuracy of themagnetic sensor array 308 is verified (e.g., the accuracy of themeasurements of the magnetic sensors 350 may be verified). Suchverification process may be executed before each registration procedureor as part of a maintenance routine such as a monthly or weeklymaintenance procedure. To verify the accuracy of the magnetic sensorarray 308, a test apparatus 440 may be coupled to the sensing headportion 332 of the magnetic sensor array 308 as illustrated in FIG. 30.The test apparatus 440 includes a frame 442 and a magnetic sourcehousing 444. A test magnetic source 446 is located in the housing 444.The frame 442 has a number of mounting apertures 448. The magneticsource housing 444 may be mounted to the frame 442 via the apertures 448and mounting devices 449, such as screws or bolts. Because the frame 442includes a number of mounting apertures 448, the housing 444, andthereby the test magnetic source 446, may be positioned at a number ofdifferent distances from the sensing head portion 332. Accordingly,because the magnetic flux density (or magnetic strength) of the testmagnetic source 446 is known and the distance of the source 446 from thesensing head portion 332 (i.e., from the sensor circuit 328 located inthe sensing head 332) is known, an expected magnetic flux densitymeasurement value for each magnetic sensor 350 can be determined. Theactual measured magnetic field values of each magnetic field sensor 350(i.e., the output voltage levels of the magnetic sensors 350 indicativeof one or more axes of the three-dimensional magnetic flux densitycomponents at each sensor's position) may then be compared to theexpected magnetic flux density values. Any error above a predeterminedthreshold may be indicative of malfunction of the magnetic sensor array308. To further improve the verification procedure, expected andmeasured magnetic flux density values may be determined for eachlocation of the magnetic source housing 444 on the frame 442. Theillustrative test apparatus 440 is but one embodiment of a testapparatus which may be used with the magnetic sensor array 308. In otherembodiments, test apparatuses having other configurations may be used.

Next, in process step 404, the magnetic source 309 is coupled to therelevant bony anatomy of the patient. The magnetic source 309 may beimplanted in or otherwise fixed to the bone or bones of the patient uponwhich the orthopaedic surgical procedure is to be performed. Forexample, if a total knee arthroplasty (TKA) surgical procedure is to beperformed, one or more magnetic sources 309 may be coupled to therelevant tibia bone, the relevant femur bone, or both the relevant tibiaand femur bones of the patient. As discussed above, each magnetic source309 may be embodied as one or more magnets 450.

The magnet(s) 450 which embody the magnetic source 309 may be coupled tothe bone of the patient using any suitable fixation means that securesthe magnet(s) 450 to the bone such that the magnet(s) 450 do not move orotherwise propagate about before and during the performance of theorthopaedic surgical procedure. In one embodiment, the magnet(s) 450 arecoupled to the bone of the patient by implanting the magnet(s) 450 inthe bone. To do so, as illustrated in FIG. 31, an implantable capsule460 may be used. The capsule 460 includes a body portion 462 in which amagnet 450 is located and a threaded screw portion 464 at a distal endof the body portion 462. The capsule 460 may be formed from anynonmagnetic material, such as a plastic material, such that the magneticfield generated by the magnet 450 is not degraded by the capsule 460. Asshown in FIG. 32, the capsule 460 (and the magnet 450) may be implantedin a bone 466 of the patient by first boring a suitable hole into thebone and subsequently inserting the capsule 350 by, for example,screwing the capsule 350 into the bored hole. In other embodiments,implantable capsules having other configurations may be used. Forexample, in some embodiments, the implantable capsule may includethreads that cover the entire body of the capsule.

As discussed above in regard to FIG. 23, the position of the magnet 450once coupled to the bone of the patient is defined by six degrees offreedom. However, because the magnetic field of the illustrative magnet450 is circumferentially symmetric about the magnet 450, only fivedegrees of freedom can be determined using a single illustrative magnet450 as the magnetic source 309. That is, the values for the threeCartesian coordinates (i.e., X-coordinate, Y-coordinate, andZ-coordinate values of FIG. 23) and two rotational values (i.e., the(theta) θ-rotational value about the X axis and the (phi) φ-rotationalvalue about the Y axis of FIG. 23) can be determined. To provide for thedetermination of the sixth degree of freedom (i.e., the (psi)ψ-rotational value about the Z axis of FIG. 23), at least one additionalmagnet 450 may be used.

The two or more magnets 450 that form the magnetic source 309 may becoupled or implanted into the bone of the patient at any angle withrespect to each other. Due to bone density inconsistencies and otherfactors the three angles (theta, phi, and psi) between the magnets 450may be uncontrollable and, therefore, unknown. In such embodiments, thesixth degree of freedom of the magnetic source may be determined basedon images of the bone(s) and the magnetic source 309 coupled thereto asdiscussed in detail below in regard to algorithm 800.

In other embodiments, the magnets 450 may be coupled or implanted intothe bone of the patient at a predetermined, known position (locationand/or rotation) relative to each other. For example, the two magnets450 may be implanted into the bone of the patient such that the magnets450 are substantially orthogonal to each other. Because the magneticfields of the two magnets 450 have different magnetic field vectors dueto the difference in orientation and because the angle between themagnets 450 is known, the six degrees of freedom of the magnetic source309 (i.e., the two magnets 450) may be determined based on the measuredfive degrees of freedom of each magnet 450 and the known position of themagnets 450 relative to each other.

Regardless as to the angles of rotation defined between the magnets 450,the magnets 450 are implanted a distance apart from each other such thatthe magnetic fields generated by the magnets 450 do not interfere witheach other. That is, the magnets 450 are separated by a sufficientdistance such that the magnetic field of one magnet 450 does notconstructively or destructively interfere with the magnetic field ofanother magnet 450. In one particular embodiment, the magnets 450 areimplanted a distance of two times or more the maximum desired measuringdistance (e.g, the maximum Z-axis distance from the magnets 450 that themagnetic sensor array 308 can be positioned while still accuratelymeasuring the magnetic field of the magnets 450).

In some embodiments, a jig or guide may be used to facilitate theimplanting of two or more magnets 450 at a predetermined distance fromeach other (and predetermined angles of rotation relative to each otherif so desired). For example, as illustrated in FIG. 33, a jig 470 may beused to facilitate the implanting of two magnets 450 into a bone 472 ofthe patient. The jig 470 includes a frame 474 having a first mountingpad 476 and a second mounting pad 478. The mounting pads 476, 478 arepositioned at a predetermined set of rotation angles in three dimensionswith respect to each ensuring the desired rotational configurationbetween the magnets 450. In the illustrative jig 470, the mounting pads476, 478 are positioned substantially orthogonal to each other aboutonly one axis of a three-dimensional coordinate system such that themagnets 450 implanted using the jig 470 will be implanted substantiallyorthogonal to each other about this single axis. The mounting pad 476includes a mounting aperture 482. Similarly, the mounting pad 478includes a mounting aperture 484. The apertures 482, 484 are separatedfrom each other by a distance 486 equal to the desired distance of themagnets 450 once implanted into the bone 472. As such, the apertures482, 484 may be used as guides when implanting the magnets 450 (i.e.,the magnets 450 may be implanted through the apertures 482, 484) suchthat the magnets 450 are implanted into the bone 472 ensuring apredetermined configuration (i.e., location and orientation with respectto each other and the bone 472).

In some embodiments, the jig 470 may also include a handle 490 coupledto the frame 474 to allow the positioning of the jig 470 by the surgeon.Alternatively, the jig 470 may be secured to a rigid body such as asurgical table to reduce the likelihood that the jig 470 moves orbecomes repositioned between or during the implantation of each magnet450. Although the illustrative jig 470 is illustrated in FIG. 32 asbeing abutted or next to the bone 472 of the patient, it should beappreciated that in use the jig 470 may be positioned on the outside ofthe skin of the patient such that only incisions or punctures for themounting holes 482, 484 need to be made. In this way, the magnets 450may be implanted into the bone of the patient ensuring a predeterminedconfiguration (i.e., location and orientation with respect to each otherand the bone 472) with reduced surgical exposure to the patient.

In yet other embodiments, the two or more magnets 450 that form themagnetic source 309 may be secured to each other via a fixed brace orsupport member. The support member secures the magnets 450 at apredetermined three-dimensional position (i.e., location andorientation) with respect to each other. In such embodiments, the jig470 may not be required. However, because the magnetic source 309 isstructurally larger in such embodiments, a larger incision may berequired to implant the magnetic source 309 into the bone of thepatient.

In embodiments wherein the magnetic source 309 is formed from two ormore magnets 450, the magnetic sensor array 308 may be used bypositioning the array 308 (i.e., the sensor circuit 328) in the magneticfield of the one of the magnets 450, sensing the magnetic field of thethat magnet 450 to determine position data indicative of its positionrelative to the magnetic sensor array 308, and then positioning themagnetic sensor array 308 in the magnetic field of the next magnet 450relative to the magnetic sensor array 308, sensing the magnetic field ofthe next magnet 450, and so on.

Alternatively, as illustrated in FIG. 34, a magnetic sensor array 500may be used. The magnetic sensor array 500 includes a frame 502 and twosensing head portions 504, 506. The head portions 504, 506 arepositioned a distance 512 from each other. The distance 512 issubstantially equal to the distance 486 by which the magnets 450 areseparated after being implanted into the bone 472 of the patient. Eachsensing head portion 504, 506 includes a sensor circuit 510, which issimilar to the sensor circuit 328 of the magnetic sensor 308. Themagnetic sensor array 500 also includes a reflective sensor array 514,which is similar to the reflective sensor array 336 of the magneticsensor array 308. The reflective sensor array 514 includes a number ofreflective elements 516 and is used by the controller 302 to determinethe relative position of the magnetic sensor array 500.

Additionally, the magnetic sensor array 500 includes a handle 508 toallow positioning of the magnetic sensor array 500. That is, a surgeoncan use the handle 508 to position the magnetic sensor array 500 suchthat each of the head portions 504, 506, and the respective sensorcircuits 510, are each positioned in a magnetic field of one of themagnets 450. Because the distance 512 between the sensing head portions504, 506 is substantially equal to the distance 486 between the magnets450, each of the head portions 504, 506 may be positioned in themagnetic field of one of the magnets 450 at the same time. In this way,the magnetic sensor array 500 may be used to measure the magnetic fieldof the two magnets 450, which embody the magnetic source 309,simultaneously or contemporaneously rather than measuring one magneticfield and then the next magnetic field as done when using the magneticsensor array 308. In some embodiments, the sensing head portions 504,506 may be configured to pivot with respect to the frame 502 so as toadjust the distance 512 and accommodate a variety of distances 486between the magnets 450.

Referring now back to FIG. 24, after the magnetic source 309 has beencoupled to the bone of the patient in process step 404, an image of thebone or bones having the magnetic source 309 coupled thereto isgenerated in process step 406. It should be appreciated that themagnetic source 309 is coupled to the bone of the patient prior to theperformance of the orthopaedic surgical procedure. As such, the magneticsource 309 may be coupled to the bone of the patient well in advance ofthe date or time of the orthopaedic surgical procedure or immediatelypreceding the procedure. Accordingly, the image of the bone or bonyanatomy of the patient may be generated any time after the coupling stepof process step 404. For example, the bone(s) of the patient may beimaged immediately following process step 404, at some time after thecompletion of process step 404, or near or immediately preceding theperformance of the orthopaedic surgical procedure.

The relevant bone(s) of the patient (i.e., the bone(s) which have themagnetic source 309 coupled thereto) may be imaged using any suitablebony anatomy imaging process. The image so generated is athree-dimensional image of the relevant bone(s) of the patient andincludes indicia of the magnetic source 309 coupled to the bone(s). Thatis, the image is generated such that the position (i.e., location andorientation) of the magnets 450 implanted or otherwise fixed to therelevant bone(s) is visible and/or determinable from the image. To doso, any image methodology capable of or usable to generate athree-dimensional image of the relevant bone(s) and magnetic source 309may be used. For example, computed tomography (CT), fluoroscopy, and/orX-ray may be used to image the bone.

In one particular embodiment, two non-coplanar X-ray images are used toform a three-dimensional image of the relevant bone(s) and magneticsource 309. To do so, as illustrated in FIG. 25, an algorithm 800 forgenerating an image of the relevant bony anatomy may be used. Thealgorithm 800 begins with process step 802 in which a first X-ray imageof the relevant bony anatomy is generated. The first X-ray imageincludes indicia of the magnetic source 309. Next, in process step 804,a second X-ray image of the relevant bony anatomy and magnetic source309 is generated. It should be appreciated that the first and secondX-ray images are generated such that the first and second X-ray imagesare non-coplanar with each other.

Subsequently, in process step 806, a three-dimensional image of therelevant bone and magnetic source 309 is generated based on the firstand second X-ray images. As discussed above, the first and second X-rayimages are non-coplanar and may be compared with each other to determinethe three-dimensional image. To do so, anytwo-dimensional-to-three-dimensional morphing algorithm may be used. Forexample, any one or combination of the morphing algorithms disclosed inU.S. Pat. No. 4,791,934, U.S. Pat. No. 5,389,101, U.S. Pat. No.6,701,174, U.S. Patent Application Publication No. US2005/0027492, U.S.Patent Application Publication No. US2005/0015003A1, U.S. PatentApplication Publication No. US2004/021571, PCT Patent No. WO99/59106,European Patent No. EP1348394A1, and/or European Patent No. EP1498851A1may be used.

Once the three-dimensional image of the relevant bone(s) and magneticsource 309 coupled thereto has been generated, data indicative of thepositional relationship between the magnetic source 309 (i.e., the twoor more magnets 450) and the bone(s) is determined in process step 808.To do so, a computer or computing device (such as the controller 302, acomputer couple to the imaging device, or other computer or processingdevice) may execute an image analysis algorithm to determine, forexample, the centroid and orientation of the magnets 450 forming themagnetic source 309 (i.e., the position of the magnets to five degreesof freedom) and vector data relating such centroid to the surfacecontours and/or fiducial points of the relevant bone(s). As such, thedata indicative of the positional relationship between the magneticsource 309 and the relevant bone(s) may be embodied as a collection ofvectors, scalar data, equations, or the like. As discussed below inregard to algorithm 420, such data is used by the controller 302 inconjunction with the position data received from the magnetic sensorarray 309 to determine the location and orientation of the relevantbone(s).

In some embodiments, a matrix of components defining the translationsand rotations relating the position of the first magnet 450 to thesecond magnet 450 is determined in process step 810. Typically, in suchembodiments, the magnets 450 were implanted or coupled to the relevantbones without the use of a jig or the like such that the positionalrelationship between the magnets 450 is unknown at the time ofimplantation. However, in process step 810, the translation and rotationmatrix may be determined based on the three-dimensional image generatedin process step 806. To do so, a computer or computing device (such asthe controller 302, a computer couple to the imaging device, or othercomputer or processing device) may be configured to determine the fivedegrees of freedom of each magnet 450 identified in thethree-dimensional image. The five degrees of freedom of the magnets 450may be determined in reference to any coordinate system. In oneparticular embodiment, the five degrees of freedom of the magnets 450 isdetermined in reference to a coordinate system defined by the relevantbone(s). To do so, data indicative of the positional relationshipbetween the magnetic source 309 and the relevant bone(s) as determinedin process step 808 may be used. Once the five degrees of freedom foreach magnet 450 have been determined, these values are compared todetermine a 1×5 matrix including the three components of the translationvector between the centroids of the magnets 450 and two angularrotations defining the spatial relationship between the two magnets 450.The matrix, therefore, defines the magnetic source 309. Once sodetermined, the matrix may be stored by the controller 302 in, forexample, the memory device 316 or the database 318, 320. Thetranslation/rotation matrix may be used in later computations todetermine the six degrees of freedom of the magnetic source as discussedin more detail below in regard to algorithm 420.

Subsequently, in process step 812, the three-dimensional images andassociated data, such as the data determined in steps 808 and 810, arestored. In one embodiment, the images and associated data are stored bythe controller 302 in the memory device 316, the database 318, and/orthe remote database 320 (shown in FIG. 18), which as discussed above mayform a portion of the hospital network and be located apart form thecomputer assisted orthopaedic surgery (CAOS) system 301. In suchembodiments, the controller 302 may be configured to retrieve thethree-dimensional images from the remote database 320 when required forprocessing. In other embodiments, the three-dimensional images may bestored in a database or other storage location that is not incommunication with the controller 302. In such embodiments, thethree-dimensional images may be supplied to the controller 302 whenrequired via a portable media such as a compact disk, a flash memorycard, a floppy disk, or the like.

The three-dimensional images may be stored in any format thatfacilitates later retrieval and/or regeneration of the three-dimensionalimage. For example, the three-dimensional image may be stored as acollection of vector data usable to recreate the three-dimensionalimage. Alternatively, only particular points defining the contours ofthe relevant bone and the magnetic source 309 may be stored. In suchembodiments, an algorithm may be used later to recreate the relevantbone(s) and magnetic source using the stored data points.

Although the illustrative algorithm 800 utilizes two non-coplanar X-rayimages of the relevant bone(s) and magnetic source 309, other imagingmethods may be used in other embodiments. For example, a computedtomography scan may be used to generate a three-dimensional image of therelevant bone(s) and magnetic source 309 coupled thereto. As withtypical computed tomography technology, a three-dimensional image isgenerated from a plurality of two-dimensional images produced from thecomputed tomography scan. Utilizing appropriate software filters andimaging algorithms, the counters of the relevant bones, the position ofthe magnetic source 309, and the positional relationship between themagnetic source 309 and the relevant bone(s) may be determined based onthe computed tomography, three-dimensional image in a manner similar tothat used in the algorithm 800 described above.

Referring back to FIG. 24, once the relevant bony anatomy has beenimaged in process step 406, errors due to the magnetic sensors 350themselves may be determined and compensated for in process step 407.Due to manufacturing tolerances, ageing, damage, use, and other factors,the magnetic sensors 350 may generate an offset output signal (i.e.,offset voltage) in the absence of a magnetic field. If the offset outputsignal of the magnetic sensors 350 is known, the accuracy of themagnetic sensor 308 can be improved by subtracting the offset of themagnetic sensors 350 from the measurements of the magnetic sensors 350.To do so, the magnetic sensor array 308 may be positioned in amagnetically shielded case or housing. The magnetically shielded case isconfigured to block a significant amount of outside magnetic fields suchthat the environment contained inside the case is substantially devoidof any magnetic fields. In one embodiment, the magnetically shieldedcase is formed from a mu-metal material such as particular nickelalloys, from ceramics, or from other materials having suitable shieldingproperties. To compensate for the offset voltage of the magnetic sensors350, the magnetic sensor array 308 may be positioned in the magneticallyshielded case and operated remotely, or autonomously via an errorcompensation software program, to measure the output signals of themagnetic sensors 350. Because there is no significant magnetic fieldinside the magnetically shielded case, the output signals of themagnetic sensors 350 are indicative of any offset voltage errors. Oncethe offset voltage errors are so determined, the accuracy of themagnetic sensor array 308 may be improved. That is, the sensor circuit328 may be configured to subtract such offset voltages from themeasurements of the magnetic sensors 350 to thereby account for theoffset errors. It should be appreciated that the process step 407 may beperformed any time prior to the performance of the registration of thebone or bony anatomy (see process step 410 below). In one particularembodiment, the process step 407 is executed just prior to theregistration of the relevant bone(s) such that the reduced time lapsebetween the process step 407 and the registration process reduces thelikelihood that the errors drift or change.

Subsequently, the magnetic sensor array 308, 500 is registered with thecontroller 302 in process step 408 and a navigation sensor array iscoupled to the relevant bony anatomy in process step 409. As shown inFIG. 24, the process steps 408, 409 may be executed contemporaneouslywith each other or in any order. Unlike process steps 404 and 406, theprocess step 408 is typically performed immediately prior to theperformance of the orthopaedic surgical procedure. To register themagnetic sensor array 308, 500, the array 308, 500 is positioned in thefield of view 52 of the camera unit 304 such that the reflective sensorarray 336, 514 is viewable by the camera unit 304. Appropriate commandsare given to the controller 302 such that the controller 302 identifiesthe magnetic sensor array 308, 500 via the reflective sensor array 336,514 coupled thereto. The controller 302 is then capable of determiningthe position of the magnetic sensor array 308, 500 using the reflectivesensor array 336, 514.

In process step 409, a navigation sensor array is coupled to therelevant bone or bones of the patient. The navigation sensor array issimilar to sensor array 54 illustrated in and described above in regardto FIG. 2. Similar to sensor array 54, the navigation sensor array maybe a reflective sensor array similar to reflective sensor arrays 336 and514 or may be an electromagnetic or radio frequency (RF) sensor arrayand embodied as, for example, a wireless transmitter. Regardless, thenavigation sensor array is coupled to the relevant bony anatomy of thepatient such that the navigation sensor array is within the field ofview of the camera unit 304. The controller 302 utilizes the navigationsensor array to determine movement of the bony anatomy once the bonyanatomy has been registered with the computer assisted orthopaedicsurgery (CAOS) system 301 as discussed below in regard to process step410.

After the magnetic sensor array 308, 500 has been registered with thecontroller 302 in process step 408 and the navigation sensor array hasbeen coupled to the relevant bony anatomy, the bone or bony anatomy ofthe patient having the magnetic source 309 coupled thereto is registeredwith the controller 302 in process step 410. To do so, as illustrated inFIG. 26, an algorithm 820 for operating a magnetic sensor array 308, 500may be used. The algorithm 820 will be described below in regard to amagnetic source 309 embodied as two magnets 450 with the understandingthat the algorithm 820 may be used and/or readily adapted for use withmagnetic sources embodied as any number of magnetic sources.

The algorithm 820 begins with process step 822 in which the magneticsensor array 308, 500 is positioned. If the magnetic sensor array 308 isused, the magnetic sensor array 308 is positioned in the magnetic fieldof the first magnet 450 in process step 822 such that the sensor circuit328 of the magnetic sensor array 308 is positioned over a magneticmoment of the magnet 450. In one particular embodiment, the magneticsensor array 308 may be positioned such that the central magnetic sensor350 ₁ (see FIG. 20) is substantially on-axis with the magnetic moment ofthe magnet 450. To do so, the sensor circuit 328 may be configured tomonitor the output of the magnetic sensor 350 ₁. For example, in theillustrative embodiment, the sensor circuit 328 may be configured tomonitor the X-component and the Y-component outputs of the centrallylocated, three-dimensional magnetic sensor 350 ₁. The magnetic sensorarray 308 is determined to be positioned over the magnetic moment of themagnet 450 (i.e., the field sensitive point of the magnetic sensor 350 ₁is on-axis or near on-axis with the magnetic moment of the magnet 450)when the measured X-component and Y-component measurements are at aminimum value (or below a threshold value).

In other embodiments, sensor circuit 328 may be configured to monitorthe X-component and the Y-component outputs of additional magneticsensors 350. For example, the sensor circuit 328 may be configured tomonitor the output of all magnetic sensors 350 configured to measure theX-component of the three-dimensional magnetic flux density of the magnet450 at a given position (e.g., magnetic sensors 350 ₁-350 ₅, 350 ₁₅, and350 ₁₇) and the output of all the magnetic sensors 350 configured tomeasure the Y-component of a three-dimensional magnetic flux density ofthe magnet 450 at a given position (i.e., magnetic sensors 350 ₁-350 ₅,350 ₁₄, and 350 ₁₆). For example, the sensor circuit 328 may beconfigured to sum the output of such sensors and determine the locationat which such sums are at a minimum value.

To assist the surgeon in positioning the magnetic sensor array 308, thesensor circuit 328 may be configured to provide feedback to the surgeonvia the indicator 360. For example, when the sensor circuit 328determines that the sum of the X-component measurements and the sum ofthe Y-component measurements have reached minimum values, the sensorcircuit 328 may be configured to activate the indicator 360. In thisway, the surgeon knows when the magnetic sensor array is properlypositioned in the X-Y plane relative to the magnet 450.

In other embodiments, the sensor circuit 328 may be configured to adaptto non-alignment of the magnetic sensor array 308. For example, based onthe X-component and Y-component measurement outputs of the magneticsensors 350 ₁-350 ₅ and 350 ₁₄-350 ₁₇, the sensor circuit 328 may beconfigured to determine which magnetic sensor 350 is on-axis or closestto on-axis with the magnetic moment of the magnet 450. For example, ifthe X-component and Y-component measurement outputs of the magneticsensor 350 ₅ (see FIG. 20) is near zero or at a minimum, the sensorcircuit 328 may be determine that the field sensitive point of themagnetic sensor 350 ₅ is on-axis or near on-axis with the magneticmoment of the magnet 450. Rather than forcing the surgeon or user toreposition the magnetic sensor 308, the sensor circuit 328 may beconfigured to adjust measurement values of the magnetic sensors 350 forthe X-Y offset of the magnetic moment of the magnet 450 relative to thesensor board 370.

In process step 822, the magnetic sensor array 308 is also positionedalong the Z-axis relative to the magnet 450. That is, the magneticsensor array 308 is positioned a distance away from the magnet 450 alongthe Z-axis as defined by the magnetic moment of the magnet 450. Themagnetic sensor array 308 is position at least a minimum distance awayfrom the magnet 450 such that the magnetic sensors 350 do not becomesaturated. Additionally, the magnetic sensor array 308 is positionedwithin a maximum distance from the magnet 450 such that the measuredmagnetic flux density is above the noise floor of the magnetic sensors350 (i.e., the magnetic flux density if sufficient to be discerned bythe magnetic sensors 350 from background magnetic “noise”). The sensorcircuit 328 may be configured to monitor the output of the magneticsensors 350 to determine whether the magnetic sensors 350 are saturatedor if the output of the magnetic sensors 350 is below the noise floor ofthe sensors 350. The sensor circuit 328 may be configured to alert thesurgeon or user of the magnetic sensor array 308 if the magnetic sensorarray 308 is properly positioned with respect to the Z-axis relative tothe magnet 450. As discussed above in regard to process step 404 ofalgorithm 400, the maximum distance at which the magnetic sensor array308 will be used also determines the minimum distance between theindividual magnets 450 that form the magnetic source 309 (i.e., themagnets 450 are separated by a distance of two times or more the maximummeasurement distance of the magnetic sensor array 308 in oneembodiment).

Alternatively, the magnetic sensor array 500 may be used to register thebone(s) of the patient by positioning the array 500 such that each ofthe sensing heads 504, 506 (and sensor circuits 510) is positioned in amagnetic field of one of the magnets 450. That is, the magnetic sensorarray 500 is positioned such that each sensor circuit 510 is on-axiswith the magnetic moment of the respective magnet 450. As discussedabove in regard to the magnetic sensor array 308, each of sensing heads504, 506 may be positioned such that a central magnetic sensor 350 ₁ issubstantially on axis with the magnetic moment of each magnet 450. To doso, each sensor circuit 510 may be configured to monitor the X-componentand Y-component measurement outputs of the respective magnetic sensor350, and determine when such measurements are at a minimum magnitude orbelow a predetermined threshold. Alternatively, as discussed above inregard to the magnetic sensor array 308, the sensor circuits 510 may beconfigured to adapt to non-alignment of the sensor circuits 510 withrespect to the magnets 450 by determining which individual magneticsensor 350 is on-axis or closest to on-axis with the magnetic moments ofthe magnets 450 and adjusting the magnetic field measurements of theremaining magnetic sensors 350 accordingly. Further, similar to magneticsensor array 308, the sensor circuits 510 of the magnetic sensor array500 may be configured to determine when the magnetic sensor array 500 isproperly positioned in the Z-axis with respect to the magnets 450. Thatis, the sensor circuits 510 may be configured to monitor the output ofthe magnetic sensors 350 to determine whether the magnetic sensors 350are saturated or if the output of the magnetic sensors 350 are below thenoise floor of the sensors and determine if the magnetic sensor array500 is properly positioned based thereon.

Once the magnetic sensor array 308, 500 has been properly positioned,the position of the magnetic source 309 (i.e., the magnets 450) withrespect to the magnetic sensor array 308, 500 is determined in processstep 824. To do so, the magnetic sensor array 308, 500 (i.e., sensorcircuits 328, 510) may execute an algorithm 830 for determining aposition of a magnetic source as illustrated in FIG. 27.

The algorithm 830 begins with process steps 831 and 832. As illustratedin FIG. 27, the process steps 831 and 832 may be executedcontemporaneously with each other or in any order. In process step 831,undesirable environmental magnetic fields which may cause errors in themeasurements of the magnetic sensors 350 are measured. The accuracy ofthe measurements of the magnetic sensors 350 may be improved bycompensating the magnetic sensor array 308 for these undesirable,adverse factors. The environmental magnetic fields which are measured inprocess step 831 may include the Earth's magnetic field and magneticfields generated from other equipment located in the surgical room,electrical cables, iron constructions, vehicles, and other stray orundesirable magnetic fields generated by sources other than the magneticsource 309 which may interfere with the magnetic fields generated by themagnetic source 309. For example, the Earth's magnetic field mayadversely affect the measurements of the magnetic sensors 350 byinterfering (i.e., constructively or destructively) with the magneticfield generated by the magnetic source 309. Because the Earth's magneticfield is continuously changing, a fixed adjustment value or offset forthe magnetic sensors 350 is not available. However, as discussed abovein regard to FIGS. 21 and 22, by using a remote magnetic sensor 386, theeffects of the Earth's magnetic field can be accounted for. That is,because the remote magnetic sensor 386 is located apart from the sensorcircuit 328 of the magnetic sensor array 308, the magnetic fieldgenerated by the magnetic source 309 has minimal impact on themeasurements of the remote magnetic sensor 386. As such, themeasurements of the remote magnetic sensor 386 are generated primarilyin response to the Earth's magnetic field and other environmentalmagnetic fields such as those caused by other surgical equipment locatedin the operating room and the like. Therefore, in process step 831, themeasurements of the remote magnetic sensor 386 are sampled.

In process step 832, the components of the three-dimensional magneticflux density of the magnet 450 at various positions is measured. To doso, the output of each of the magnetic sensors 350 is sampled. Asdiscussed above in regard to FIG. 20, some of the magnetic sensors 350are three-dimensional magnetic sensors and, as such, measure themagnitude of each component at a given position of the magnetic fluxdensity of the magnet 450. Other magnetic sensors 350 areone-dimensional magnetic sensors and are configured to measure themagnitude of only one component of the magnetic flux density. In theillustrative embodiment of FIG. 20, a total of twenty seven componentmeasurements are generated by the magnetic sensors 350 (i.e., fivethree-dimensional magnetic sensors and twelve one-dimensional magneticsensors). The magnetic field measurements may be stored in a suitablememory device for subsequent processing as described below. The samplingrate of the magnetic sensors 350 may be of rate useable or sustainableby the processing circuit 352

Contemporaneously with or during predetermined periods of themeasurement process of the magnetic sensors 350 (e.g., during thepositioning of the magnetic sensor array 308 in process step 822 of thealgorithm 820 or during the process step 832 of algorithm 830), thesensor circuit 328 may be configured to perform a number of testprocedures. To do so, the sensor circuit 328 may include one or moretest circuits configured to perform one or more test algorithms. Forexample, the test circuits may be configured to measure the supplyvoltage of the sensor circuit 328 and produce an error if the supplyvoltage is below a predetermined minimum threshold or above apredetermined maximum threshold. Additionally, the sensor circuit 328may be configured to monitor the output of the magnetic sensors 350 andproduce an error (e.g., activate an indicator to alert the user of themagnetic sensor array 308) if the voltage levels of the output signalsof the sensors 350 are above a predetermined maximum threshold (i.e.,the magnetic sensors 350 are in saturation) or below a predeterminedminimum threshold (i.e., below the noise floor of the magnetic sensors350). Additionally, in some embodiments, the sensor circuit 328 mayinclude one or more compensation circuits to compensate or adjust themeasurement values of the magnetic sensors 350 for such factors astemperature or the like.

Subsequently, in process step 833, the measurements of the magneticsensors 350 are compensated or adjusted for the undesirableenvironmental magnetic fields. To do so, in one embodiment, themeasurements of the magnetic sensors 350 are adjusted by subtracting themeasurements of the remote magnetic sensor 386. In this way, themagnetic field errors caused by the Earth's magnetic field and otherenvironmental magnetic fields are adjusted out of the measurement dataproduced by the magnetic sensors 350 and the overall accuracy of themagnetic sensor array 308 in measuring the magnetic flux densitygenerated primarily from the magnetic source 309 is improved.

In process step 834, an initial estimate of the position of the magnet450 is determined. The initial estimate includes an estimate of thevalues of the five degrees of freedom of the magnet 450. That is, theinitial estimate includes an X-coordinate value, a Y-coordinate value, aZ-coordinate value, a (theta) θ-rotational value about the X-axis, and a(phi) φ-rotational value about the Y-axis of the magnet 450. In oneparticular embodiment, the X-, Y-, and Z-coordinate values are thecoordinate values of the particular magnetic sensor 350 with respect tothe centroid of the magnet 450. That is, the X-, Y-, and Z-coordinatevalues are estimates of the position of the magnetic sensor 350 in athree-dimensional coordinate system wherein the centroid of the magnet450 is defined as the center of the coordinate system (i.e., thecentroid of the magnet 450 lies at point (0, 0, 0)). Estimating thelocation of the magnet 450 in this manner allows calculations of themagnetic flux density using positive values for the X-, Y-, andZ-coordinate estimated values.

The estimated values may be any values and, in some embodiments, arepredetermined seeded values that are used for measurement processes.However, by selecting an initial estimate closer to the actual positionof the magnet 450, the speed and accuracy of the algorithm 830 may beimproved. To do so, knowledge of the position of the magnetic sensorarray 308, 500 with respect to the magnet 450 may be used. That is, asdiscussed above in process step 822 of algorithm 820, the magneticsensor arrays 308, 500 are positioned such that the arrays 308, 500 areon-axis or near on-axis with the magnetic moment of the magnet 405. Assuch, in one embodiment, the initial estimate of the location of themagnet 405 with respect to the magnetic sensor array 308, 500 includesan estimated X-coordinate value of zero and an estimate Y-coordinatevalue of zero. Additionally, the (theta) θ-rotational value and the a(phi) φ-rotational value of the magnet 450 may be estimated as zero(e.g., it may be assumed that the sensor board 370 of the magneticsensor array 308, 500 is positioned orthogonal to the longitudinal axisof the magnet 405). The Z-coordinate value may also be estimated atzero. However, for additional accuracy, the Z-coordinate value may beestimated based on the average magnetic flux density of the Z-vector ofthe magnetic flux density of the magnet 450 as measured by the magneticsensors 350 (i.e., those magnetic sensors 350 configured to measure theZ-vector of the three-dimensional magnetic field of the magnet 450).However, other estimated values may be used in other embodiments.

Once the initial estimated position of the magnet 450 is determined inprocess step 834, the components of the theoretical three-dimensionalmagnetic flux density of the magnet 450 at various points in space arecalculated in process step 836. During the first iteration of thealgorithm 830, the five degrees of freedom values of the magnet 450estimated in process step 834 are used to determine each component ofthe theoretical three-dimensional magnetic flux density. However, asdiscussed below in regard to process step 842, in subsequent iterationsof the algorithm 830, revised estimated values of the five degrees offreedom of the magnet 450 are used in process step 836.

The theoretical three-dimensional magnetic flux density of the magnet450 at each sensor's 350 position at a point in space about the magnet450 may be calculated using any suitable equation(s) and/or algorithms.In one particular embodiment, the following equations are used tocalculate the magnitude of the magnetic flux density components (i.e.,the X-, Y-, and Z-components) of the magnet 450.$B_{x} = \frac{\mu\quad{m\left\lbrack {\frac{3{x\begin{pmatrix}{{x\quad{\sin(\Theta)}{\cos(\Phi)}} +} \\{{y\quad\sin(\Theta){\sin(\Phi)}} + {z\quad{\cos(\Theta)}}}\end{pmatrix}}}{r^{2}} - {{\sin(\Theta)}{\cos(\Phi)}}} \right\rbrack}}{4\quad\pi\quad r^{3}}$$B_{y} = \frac{\mu\quad{m\left\lbrack {\frac{3{y\begin{pmatrix}{{x\quad{\sin(\Theta)}{\cos(\Phi)}} +} \\{{y\quad\sin(\Theta){\sin(\Phi)}} + {z\quad{\cos(\Theta)}}}\end{pmatrix}}}{r^{2}} - {{\sin(\Theta)}{\cos(\Phi)}}} \right\rbrack}}{4\quad\pi\quad r^{3}}$$B_{z} = \frac{\mu\quad{m\left\lbrack {\frac{3{z\begin{pmatrix}{{x\quad{\sin(\Theta)}{\cos(\Phi)}} +} \\{{y\quad\sin(\Theta){\sin(\Phi)}} + {z\quad{\cos(\Theta)}}}\end{pmatrix}}}{r^{2}} - {\cos(\Phi)}} \right\rbrack}}{4\quad\pi\quad r^{3}}$

wherein μ is the permeability of free space (i.e., about 4*π*10⁻¹⁷WbA⁻¹m⁻¹), m is the magnitude of the magnetic moment of the magnet 450in units of Am², and r=√{square root over (x²+y^(2+z) ²)} (in distanceunits).

Once the theoretical magnetic flux densities are calculated in processstep 836, the sum of the error between the theoretical magnetic fluxdensity component values and the measured magnetic flux density valuesas determined in process step 832 is calculated in process step 838.That is, the difference between the theoretical magnetic flux densitycomponent values and the measured magnetic flux density component valuesfor each magnetic sensor 350 is calculated. The calculated differencesfor each magnetic sensor 350 is then summed. To do so, in one particularembodiment, the following objective function may be used.$F = {\sum\limits_{i = 0}^{n}{w_{i}\left( {B_{{th}_{i}} - B_{{me}_{i}}} \right)}^{2}}$

wherein n is the number of magnetic flux density components measured,B_(th) is the theoretical magnitude of the ith magnetic flux densitycomponent of the magnet 450 at a given sensor position, B_(me) is themeasured magnitude of the ith magnetic flux density component of themagnet 450 at a given position, and w_(i) is a weighting factor for theith magnetic flux density component. The weighting factor, w_(i), may beused to emphasize or minimize the effect of certain magnetic sensors350. For example, in some embodiments, the magnetic sensors 350positioned toward the center of the sensor board 370 may be given ahigher weighting factor than the magnetic sensors 350 positioned towardthe perimeter of the sensor board 370. In one particular embodiment, theweighting factors, w_(i), are normalized weighting factors (i.e., rangefrom a value of 0 to a value of 1). Additionally, other weightingschemes may be used. For example, each weighting factors, w_(i), may bebased on the magnetic field sensitivity of the particular magneticsensor 350 measuring the ith magnetic flux density component.Alternatively, the weighting factors, w_(i), may be based on thestandard deviation divided by the mean of a predetermined number ofsamples for each magnetic sensor 350. In other embodiments, theweighting factors, w_(i), may be used to selectively ignore sensors thatare saturated or under the noise floor of the magnetic sensor 350. Stillfurther, a combination of these weighting schemes may be used in someembodiments.

In process step 840, the algorithm 830 determines if the value of theobjective function determined in process step 838 is below apredetermined threshold value. The predetermined threshold value isselected such that once the objective function falls below the thresholdvalue, the position of the magnetic source 309 (i.e., the magnet 450)with respect to the magnet sensor array 308, 500 is known within anacceptable tolerance level. In one particular embodiment, thepredetermined threshold value is 0.0. However, to increase the speed ofconvergence of the algorithm 830 on or below the predetermined thresholdvalue, threshold values greater than 0.0 may be used in otherembodiments.

If the objective function (i.e., the sum of errors) is determined to bebelow the predetermined threshold value, the algorithm 830 completesexecution. However, if the objective function is determined to begreater than the predetermined threshold value in process step 840, thealgorithm advances to process step 842. In process step 842, theestimate of the position of the magnetic source is adjusted. That is, inthe first iteration of the algorithm 830, the initial estimate for theX-coordinate value, the Y-coordinate value, the Z-coordinate value, the(theta) θ-rotational value about the X axis, and the (phi) φ-rotationalvalue about the Y axis of the magnet 450 are adjusted. A localoptimization algorithm or a global optimization algorithm may be used.Any suitable local or global optimization algorithm may be used.

Once a new estimate for the position of the magnet 460 (in five degreesof freedom) has been determined, the algorithm 830 loops back to processstep 836 in which the theoretical magnetic flux density component valuesare determined using the new estimates calculated in process step 842.In this way, the algorithm 830 performs an iterative loop using thelocal/global optimization algorithm until the objective functionconverges to or below the predetermined threshold value. As discussedabove, once the objective function has so converged, the five degrees offreedom of the magnet 450 is known.

It should be appreciated that in some embodiments the algorithm 800 isexecuted solely by the magnetic sensor array 308, 500. However, in otherembodiments, the magnetic sensor arrays 308, 500 may be configured onlyto measure the magnetic flux density components of the magnet 450 inprocess step 832. In such embodiments, the process steps 834-842 areexecuted by the controller 302. To do so, the sensor circuits 328, 510of the magnetic sensor arrays 308, 500 are configured to transmit themagnetic field measurement values of each magnetic sensor 350 to thecontroller 302.

Referring now back FIG. 26, once the position (i.e., the five degrees offreedom) of each magnet 450 of the magnetic source 309 has beendetermined in process steps 822 and 824, the position data indicative ofthe five degrees of freedom of the magnetic source 309 (i.e., themagnets 450) is transmitted to the controller 302 in process step 826.The position data may be embodied as any type of data capable ofrepresenting the determined five degrees of freedom (i.e., the magnitudeof the X-coordinate value, the Y-coordinate value, the Z-coordinatevalue, the (theta) θ-rotational value, and the (phi) φ-rotational valueof the magnet(s) 450).

In response to the position data received by the magnetic sensor array308, 500, the controller 302 determines the position (i.e., the sixdegrees of freedom) of the relevant bony anatomy of the patient. To doso, the controller 302 may execute an algorithm 420 as illustrated inFIG. 28. The algorithm 420 may be embodied as software or firmwarestored in, for example, the memory device 316. The algorithm 420 beginswith process steps 422 and 426. As shown in FIG. 28, the process steps422, 426 may be executed contemporaneously with each other or in anyorder.

In process step 422, the controller 302 receives the position data fromthe magnetic sensor array 308, 500 via the communication link 326. Asdiscussed above, the position data is indicative of the position of themagnetic source 309 (i.e., the magnets 450) relative to the magneticsensor array 308, 500. In the illustrative embodiment, the position datais embodied as coefficient values that define the five degrees offreedom (i.e., X-coordinate, Y-coordinate, Z-coordinate, (theta)θ-rotational, and (phi) φ-rotational values) of the magnetic source 309.Once the position data is received from the magnetic sensor array 308,500, the controller 302 may store the position data in the memory device316.

In process step 424, the controller 302 determines the position of themagnetic sensor array 308, 500. To do so, the controller 302 receivesimages from the camera unit 304 via the communication link 310. Byanalyzing the position of the reflective sensor array 336, 514 in theimages, the controller 302 determines the position of the associatedmagnetic sensor array 308, 500 relative to the computer assistedorthopaedic surgery (CAOS) system 301 (e.g., relative to the camera 304and/or the controller 302).

Subsequently, in process step 426, the controller 302 determines theposition (i.e., to five degrees of freedom) of the magnetic source 309with respect to the computer assisted orthopaedic surgery (CAOS) system301. To do so, the controller 302 uses the position data indicative ofthe five degrees of freedom of the magnetic source 309 relative to themagnetic sensor array 308, 500 and the position of the magnetic sensorarray 308, 500 relative to the computer assisted orthopaedic surgery(CAOS) system 301 as determined in process step 424. That is, becausethe controller 302 has determined the position of the magnetic sensorarray 308, 500 within the coordinate system of the computer assistedorthopaedic surgery (CAOS) system 301 and the magnetic sensor array 308,500 has determined the position of the magnetic source 309 relative tothe array 308, 500 itself, the controller 302 can determine the positionof the magnetic source 309 in the coordinate system of the computerassisted orthopaedic surgery (CAOS) system 301 (i.e., with respect tothe CAOS system 301) by combining the two forms of position data anappropriate algorithm (e.g., a vector addition algorithm).

However, because the magnetic sensor array 308, 500 has determined onlythe five degrees of freedom of the magnetic source 309 (i.e., each ofthe magnet(s) 450 that embody the magnetic source 309), the controller302 is configured to determine the sixth degree. In furtherance thereof,in process step 428, the controller 302 retrieves the three-dimensionalimage(s) of the bony anatomy that was generated in process step 406 ofthe algorithm 400. As discussed above in regard to the process step 406,the controller 302 may retrieve the image from the database 318 and/orfrom the remote database 320. The image may be so retrieved based on anysuitable criteria. For example, in one embodiment, the image isretrieved based on patient identification data. In such embodiments, thepatient identification data may be supplied to the controller 302 priorto the performance of the orthopaedic surgical procedure. The controllermay also retrieve any number of generated images. The generated imagesinclude indicia or images of the magnetic source 309 (i.e., the twomagnets 450) and its position with respect to the bony anatomy.

In process step 430, the controller 302 creates a graphically renderedimage of the bony anatomy having a location and orientation based on theposition of the magnetic source 309 determined in process step 426 andsurface contours based on the image(s) of the bone(s) retrieved inprocess step 428. However, as discussed above, because only five degreesof freedom of the magnetic source 309 were determined and transmitted tothe controller 302 in algorithm 820, the controller 302 must determine(or retrieve) the sixth degree of freedom of the magnetic source 309. Insome embodiments, the sixth degree of freedom is already determined orknown by the controller 302. For example, in embodiments wherein themagnets 450 are implanted into the relevant bone(s) at a predeterminedangle with respect to each other, such predetermined angle may besupplied to the controller 302 as the sixth degree of freedom.Alternatively, in embodiments wherein the three dimensional image(s) ofthe relevant bony anatomy and magnetic source 309 is determined usingalgorithm 800 described above in regard to FIG. 25, the matrix locatingthe magnets 450 with respect to each other may have been determined inprocess step 810.

However, in some embodiments, the controller 302 may be configured todetermine the matrix locating the magnets 450 with respect to each otherin process step 430. To do so, the controller 302 may execute analgorithm 850 for determining the sixth degree of freedom of the magnets450 as illustrated in FIG. 29. The algorithm 850 begins with processstep 852 in which the controller 302 determines the position of a firstone of the magnets 450. The position of the magnet 450 is defined by thefive degrees of freedom of the magnet 450. The five degrees of thefreedom of the first magnet 450 with respect to the computer assistedorthopaedic (CAOS) system 301 has been determined previously by thecontroller 302 in process step 426. As such, if value(s) defining thefive degrees of freedom were stored by the controller 302, such value(s)are retrieved by the controller 302 in process step 852. Next, inprocess step 854, the controller 302 determines the position of a secondone of the magnets 450. Again, the controller 302 has already determinedthe five degrees of freedom of the second magnet 450 in process step 426and, if stored, retrieves the values indicative thereof in process step854.

Subsequently, in process step 856, the controller 302 is configured tomathematically rotate the three-dimensional image retrieved in processstep 428 of algorithm 420. The three-dimensional image is rotated aboutthe fixed position of the first magnet 450 until the position of thesecond magnet 450 is equal to the initial position, as determined instep 854, of the second magnet 450. In process step 858, the controller302 determines the sixth degree of freedom based on the amount ofrotation required. It should be appreciated that the three-dimensionalimage may be rotated about all three orthogonal axes to determine thesixth degree of freedom.

Once the six degrees of freedom of the magnetic source 309 have beendetermined, the rendered image of the bony anatomy may be generated inprocess step 430 based on the six degrees of freedom of the magneticsource 309 and the data indicative of the positional relationshipbetween the magnetic source and the bony anatomy as determined inprocess step 808. That is, because the six degrees of freedom of themagnetic source 309 are known and the positional relationship betweenthe bony anatomy and the magnetic source 309 is known, the six degreesof freedom of the bony anatomy may be determined. The rendered image maybe displayed to the surgeon or other user of the system 300 on thedisplay device 306 using the communication link 312.

Referring back to algorithm 400 in FIG. 24, after the bony anatomy hasbeen registered in process step 410, the magnetic source 309 may bedecoupled from the bone(s) of the patient in process step 412. To do so,the magnetic sensor array 308, 500 may be used to determine the locationof the magnets 450 which form the magnetic source 309. For example, themagnetic sensor array 308, 500 may be passed over the skin of thepatient until the indicator 360 of the magnetic sensor array 308, 500 isactivated, which indicates the magnetic sensor array 308, 500 is in themagnetic field of at least one of the magnets 450. The magnets 450 maythen be removed using an appropriate surgical procedure. In this way,the magnetic fields of the magnets 450 are prevented from interferingwith the performance of the orthopaedic surgical procedure. For example,in embodiments wherein the navigation sensor arrays are embodied aswireless transmitters (i.e., electromagnetic sensor arrays) rather thanreflective sensor arrays, the magnetic source 309 may be decoupled fromthe bone(s) of the patient prior to the performance of the orthopaedicsurgical procedure so as to avoid any magnetic interference with theoperation. of the sensor arrays 54. Alternatively, if the magneticsource 309 is left coupled to the bone(s) of the patient during theperformance of the orthopaedic surgical procedure, the bone(s) may bereregistered at any time and as often as necessary during the procedure.

Subsequently, in process step 414, the orthopaedic surgical proceduremay be performed. The orthopaedic surgical procedure is performed usingthe images of the relevant bony anatomy, which are displayed on thedisplay device 306 in a position and orientation based on the visualdata received from the navigation sensor array coupled to the bonyanatomy, the relative orientation and position with respect to thenavigation sensor array being determined based on the position datareceived from the magnetic sensor array 308, 500, and the generatedimages of the bony anatomy having indicia of the position of themagnetic source 309 coupled therewith. The surgeon may use the system300 to navigate and step through the orthopaedic surgical process in asimilar manner as the CAOS system 10 illustrated in and described abovein regard to FIGS. 1-17. For example, navigation with respect to thebony anatomy may be facilitated by the use of a reflective sensor array,such as one similar to the tibial array 60 of FIG. 3, coupled to thebony anatomy. It should be appreciated, however, that the presentalgorithm 400 for registering the bone anatomy of a patient maycompletely or partially replace the process step 106 of the algorithm100 illustrated in and described above in regard to FIG. 6.

Referring now to FIG. 35, in another embodiment, a magnetic sensorapparatus 600 for registering a bone of a patient with a computerassisted surgical system includes a support frame 602, a first magneticsensor array 604, and a second magnetic sensor array 606. The apparatus600 also includes a reflective sensor array 630, which is similar to thereflective sensor array 336 of the magnetic sensor array 308. Thereflective sensor array 630 includes a number of reflective elements 632and is used by the controller 302 to determine the relative position ofthe apparatus 600. The magnetic sensor array 604 includes a arm portion610 and a sensing head portion 612. Similarly, the magnetic sensor array606 includes a arm portion 614 and a sensing head portion 616. Each ofthe magnetic sensor arrays 604, 606 are movably coupled to the supportframe 602 via a coupler 608. The coupler 608 allows the magnetic sensorarrays 604, 606 to be pivoted about the support frame 602.

In addition, the magnetic sensor arrays 604, 606 may be translated withrespect to the support frame 602. For example, the head portion 612 ofthe magnetic sensor array 604 may be moved away from or toward thesupport frame 602 along a longitudinal axis 618. Similarly, the headportion 616 of the magnetic sensor array 606 may be moved away from ortoward the support frame 602 along a longitudinal axis 620. By pivotingand/or translating the magnetic sensor arrays 604, 606 with respect tothe support frame 602, each of the sensing head portions 612, 616 may bepositioned in a magnetic field generated by separate magnets coupled toa bone(s) of a patient. For example, the apparatus 600 may be used toposition the sensing heads 612, 616 in magnetic fields generated bymagnets implanted in a tibia and femur bone of a patient's leg 622 asillustrated in FIG. 35. As such, the apparatus 600 may be used to sensethe magnetic fields of a magnetic source, such as magnetic source 309embodied as a number of magnets 450, implanted in a single bone or indifferent bones of the patient. In other embodiments, the apparatus 600may include additional magnetic sensor arrays, each movably coupled tothe support frame such that magnetic fields generated by any number ofmagnets may be measured.

Each of the magnetic sensor arrays 604, 606 includes a sensor circuit650 located in the sensing head portion 612, 616 of the magnetic sensorarrays 604, 606. As illustrated in FIG. 36, each sensor circuit 650includes a magnetic sensor arrangement 651. The magnetic sensorarrangement 651 includes one or more magnetic sensors 652. Each sensorcircuit 650 also includes a processing circuit 654 electrically coupledto the magnetic sensors 652 via an interconnect 656, a transmitter 658electrically coupled to the processing circuit 654 via an interconnect660, an angle sensor 662 electrically coupled to the processing circuit654 via an interconnect 664, and a distance sensor 666 electricallycoupled to the processing circuit 654 via an interconnect 668. Theinterconnects 656, 660, 664, and 668 may be embodied as any type ofinterconnects capable of providing electrical connection between theprocessing circuit 654, the sensors 652, the transmitter 658, the anglesensor 662, and the distance sensor 666 such as, for example, wires,cables, PCB traces, or the like.

Similar to the sensor circuit 328, the number of magnetic sensors 652included in the sensor circuit 650 may depend on such criteria as thetype of magnetic sensors used, the specific application, and/or theconfiguration of the magnetic sensor arrays 604, 606. For example, thesensor circuit 650 may include any number and configuration ofone-dimensional, two-dimensional, and three-dimensional magnetic sensorssuch that the sensor circuit 650 is capable of sensing or measuring themagnetic field of the magnetic source in three dimensions.

Additionally, the magnetic sensor(s) 652 may be embodied as any type ofmagnetic sensor capable of sensing or measuring the magnetic fieldgenerated by the magnetic source. For example, the magnetic sensors 652may be embodied as superconducting quantum interference (SQUID) magneticsensors, anisotropic magnetoresistive (AMR) magnetic sensors, giantmagnetoresistive (GMR) magnetic sensors, Hall-effect magnetic sensors,or any other type of magnetic sensor capable of sensing or measuring thethree-dimensional magnetic field of the magnetic source. In oneparticular embodiment, the magnetic sensor(s) are embodied asX-H3X-xx_E3C-25HX-2.5-0.2T Three Axis Magnetic Field Transducers, whichare commercially available from SENIS GmbH, of Zurich, Switzerland. Themagnetic sensors 652 are configured to produce a number of data values(e.g., voltage levels) which define the three-dimensional magnetic fieldof the magnetic source. These data values are transmitted to theprocessing circuit 654 via the interconnects 656.

In some embodiments, the magnetic sensor arrangement 651 of each sensorcircuit 650 is substantially similar to the magnetic sensor arrangement348. For example, the magnetic sensor arrangement 651 may includeseventeen magnetic sensors 652 secured to a sensor board similar tomagnetic sensors 350 and sensor board 370 illustrated in and describedabove in regard to FIG. 20.

The processing circuit 654 may be embodied as any collection ofelectrical devices and circuits configured to determine the position ofthe magnetic source 309 relative to the magnetic sensor array 604, 606based on the data values received from the magnetic sensors 652. Forexample, the processing circuit 654 may include any number ofprocessors, microcontrollers, digital signal processors, and/or otherelectronic devices and circuits. In addition, the processing circuit 654may include one or more memory devices for storing software/firmwarecode, data values, and algorithms.

The processing circuit 654 is configured to determine position dataindicative of the position of the magnetic source 309 (e.g., magnets450) relative to the magnetic sensor array 604, 606. To do so, theprocessing circuit 654 may determine values of the five degrees or sixdegrees of freedom of the magnetic source 309. The position data may beembodied as coefficient values or other data usable by the controller302 to determine the relative position (i.e., location and orientation)of the magnetic source 309. The processing circuit 654 controls thetransmitter 658 via interconnect 660 to transmit the position data tothe controller 302 via the communication link 326.

The angle sensor 662 and the distance sensor 666 are configured tomeasure the movement of the magnetic sensor array 604, 606 and transmitthe measurements to the processing circuit 654 via the interconnects664, 668, respectively. For example, the angle sensor 662 measures anangle 672, 674 defined between a vertical reference axis 670 and themagnetic sensor array 604, 606, respectively. In this way, the anglesensor 662 determines the amount of angular distance that the magneticsensor array 604, 606 has been pivoted from the reference axis 670.Similarly, the distance sensor 666 measures a distance of translationalof the magnetic sensor arrays 612, 616 along axes 618,620, respectively.That is, the distance sensor 666 determines the amount of lineardistance that the head portions 612, 616 of the magnetic sensor arrays604, 606 have been moved along the longitudinal axes 618, 620 from areference point such as, for example, from coupler 608. The processingcircuit 654 receives the angle data and distance data from the anglesensor 662 and the distance sensor 666, respectively. The processingcircuit 654 subsequently transmits this data along with the positiondata indicative of the relative position of the magnetic source to thecontroller 302 using the transmitter 658. As such, the illustrativeapparatus 600 illustrated in FIGS. 35 and 36 includes a transmitter ineach sensor circuit 650. However, in other embodiments, the apparatus600 may include a single transmitter for transmitting all the data tothe controller 302. In such embodiments, the sensor circuit 650 themagnetic sensor arrays 604, 606 may be configured to communicate witheach other to transmit the angle data, the distance data, and theposition data determined by each sensor circuit 650.

In some embodiments, the sensor circuit 650 may also include anindicator 680. The indicator 680 may be embodied as any type ofindicator including a visual indicator, an audible indicator, and/or atactile indicator. The indicator 680 is electrically coupled to theprocessing circuit 654 via an interconnect 682, which may be similar tointerconnects 656, 660, 664, and 668. In such embodiments, theprocessing circuit 654 is configured to activate the indicator 680 whenthe magnetic sensor array 604, 606 is positioned in the magnetic fieldof a magnetic source. For example, the processing circuit 654 may beconfigured to monitor the magnetic flux density sensed by the magneticsensor(s) 652 and activate the indicator 680 when the magnetic fluxdensity reaches or surpasses a predetermined threshold value. In thisway, the magnetic sensor arrays 604, 606 may be positioned by pivotingand translating the arrays 604, 606 with respect to the support frame602 until the magnetic sensor arrays 604, 606 are positioned in amagnetic field of a magnetic source (i.e., a magnet that forms a portionof the magnetic source). Once so positioned, the indicator 680 will beactivated to notify the surgeon that the sensor arrays 604, 606 areproperly positioned.

Further, in some embodiments the sensor circuit 650 may include aregister button 684. The register button 684 may be located on anoutside surface of the magnetic sensor array 604, 606 such that thebutton 684 is selectable by a user of the apparatus 600. The button 684may be embodied as any type of button such as a push button, toggleswitch, software implemented touch screen button, or the like. Theregister button 684 is electrically coupled to the processing circuit654 via an interconnect 686, which may be similar to interconnects 656,660, 664, and 668. The functionality of the register button 684 issubstantially similar to the functionality of the register button 364 ofthe sensor circuit 328. That is, the register button 684 may be selectedby a user, such as an orthopaedic surgeon, of the apparatus 600 totransmit the position data and/or measurement values of the magneticsensors 652 to the controller 302. In some embodiments, a singleregister button 684 may be included and selectable by the orthopedicsurgeon to transmit the position data of both magnetic sensor arrays604, 606 contemporaneously with each other.

Referring now to FIGS. 37 and 38, an algorithm 700 may be used with theapparatus 600 to register a bone or bones of a patient with a CAOSsystem such as controller 302. The algorithm 700 is described below withrespect to the use of the apparatus 600 and magnetic source 309 embodiedas two magnets 450. However, other magnetic sources having any number ofmagnets may be used. Additionally, initial steps similar to processsteps 402, 404, and 406 of algorithm 400 have been omitted fromalgorithm 700 for clarity of description. However, it should beappreciated that such steps may be used with algorithm 700 as well. Forexample, the individual magnetic sensor arrays 604, 606 of the apparatus600 may be calibrated to compensate for environmental magnetic fieldeffects and/or offset voltages of the magnetic sensors 650.Additionally, the magnetic source 309 is coupled to or implanted in therelevant bony anatomy of the patient, as discussed in detail above inregard to process step 404, prior to the execution of the algorithm 700.Further, images of the bone(s) having the magnetic source 309 coupledtherewith are generated prior to the execution of the algorithm 700. Todo so, the algorithm 800 illustrated in and described above in regard toFIG. 25 may be used.

Algorithm 700 begins with process step 702 in which the apparatus 600 isregistered with the controller 302. To register the apparatus 600, theapparatus 600 is positioned in the field of view of the camera unit 304such that the reflective sensor array 630 is viewable by the camera unit304. In one particular embodiment, the apparatus 600 is secured to theceiling or a wall of the operating room or to the operating room tableupon which the orthopaedic surgical procedure will be performed. Assuch, the camera unit 304 may be positioned such that the apparatus 600is in the field of view of the camera unit 304. Appropriate commands aregiven to the controller 302 such that the controller 302 identifies theapparatus 600 via the reflective sensor array 630 coupled thereto. Thecontroller 302 is then capable of determining the relative position ofthe apparatus 600 using the reflective sensor array 630.

Once the apparatus 600 has been registered with the controller 302, thefirst magnetic sensor array 604 is positioned in process step 704. Themagnetic sensor array 604 is positioned such that the sensor circuit 650of the magnetic sensor array 604 is located in the magnetic fieldgenerated by a first magnet 450 that forms a portion of the magneticsource 309. Subsequently, in process step 706, the second magneticsensor array 606 is positioned. Similar to the magnetic sensor array604, the magnetic sensor array 606 is positioned such that the sensorcircuit 650 of the magnetic sensor array 606 is located in the magneticfield generated by a second magnet 450 that forms a portion of themagnetic source 309. The magnetic sensor arrays 604, 606 may bepositioned by moving (i.e., pivoting and translating) the arrays 604,606 about the frame 602. The magnetic sensor arrays 604, 606 may be sopositioned by using the indicators 680 of the sensor circuits 650 asdiscussed above in regard to FIG. 36.

The magnetic sensor arrays 604, 606 may be positioned in a mannersimilar to that of magnetic sensor array 308 described above in regardto algorithm 820 illustrated in FIG. 26. That is, the magnetic sensorarrays 604, 606 are positioned such that each sensor circuit 650 ison-axis with the magnetic moment of the respective magnet 450. Asdiscussed above in regard to the magnetic sensor array 308, each ofsensing head portions 612, 616 may be positioned such that a centralmagnetic sensor 652 of the magnetic sensor arrangement 651 issubstantially on axis with the magnetic moment of each magnet 450. To doso, each sensor circuit 650 may be configured to monitor the X-componentand Y-component output measurements of the central magnetic sensor 652and determine the proper positioning based on when such measurementsreach a minimum value or fall below a threshold value, as discussed inmore detail above in regard to process step 822 of algorithm 820.Alternatively, as discussed above in regard to the magnetic sensor array308, the sensor circuits 650 may be configured to adapt to non-alignmentof the sensor circuits 650 with respect to the magnets 450 bydetermining which individual magnetic sensor 652 is on-axis or closestto on-axis with the magnetic moments of the magnets 450 and adjustingthe magnetic field measurements of the remaining magnetic sensors 652accordingly.

Once the magnetic sensor arrays 604, 606 have been properly positioned,the position of the magnetic sensor arrays 604, 606 are determined inprocess steps 708, 710. To do so, in process step 708, the angle sensor662 of the sensor circuit 650 determines the angle 672, 674 definedbetween the vertical reference axis 670 and the magnetic sensor array604, 606. Additionally, in process step 710, the distance sensor 666determines the linear distance that the sensing head portion 612, 616 ofthe respective magnetic sensor array 604, 606 has been moved along therespective longitudinal axis 618, 620 from a predetermined referencepoint such as, for example, the coupler 608. The angle and distance datais subsequently transmitted to the processing circuit 654 from the anglesensor 662, and distance sensor 666, respectively.

In process step 711, a navigation sensor array is coupled to therelevant bone or bones of the patient. The navigation sensor array issimilar to sensor array 54 illustrated in and described above in regardto FIG. 2. Similar to sensor array 54, the navigation sensor array maybe a reflective sensor array similar to reflective sensor arrays 336 and514 or may be an electromagnetic or radio frequency (RF) sensor arrayand embodied as, for example, a wireless transmitter. Regardless, thenavigation sensor array is coupled to the relevant bony anatomy of thepatient such that the navigation sensor array is within the field ofview of the camera unit 304. The controller 302 utilizes the navigationsensor array to determine movement of the bony anatomy once the bonyanatomy has been registered with the computer assisted orthopaedicsurgery (CAOS) system 301 as discussed below in regard to process step712. Although process step 711 is illustrated in FIG. 37 as immediatelyfollowing process step 710, it should be appreciated that thenavigational sensor array may be coupled to the relevant bone of thepatient at any time prior to the registration of the bony anatomy inprocess step 712.

After the position of the magnetic sensor arrays 604, 606 has beendetermined, the bone or bony anatomy of the patient having the magneticsource coupled thereto is registered with the controller 302 in processstep 712. To do so, the position of the magnetic source 309 (i.e., themagnets 450) with respect to each magnetic sensor array 604, 606 isfirst determined. The magnetic sensor arrays 604, 606 (i.e., sensorcircuits 650) may execute the algorithms 830 for determining a positionof a magnetic source described above in regard to and illustrated inFIG. 27. In some embodiments, the algorithm 830 is executed solely bythe magnetic sensor arrays 604, 606. However, in other embodiments, themagnetic sensor arrays 604, 606 may be configured only to measure themagnetic field of the respective magnets 450 and transmit suchmeasurement values to the controller 302. In such embodiments, theprocess steps 834-842 of algorithm 800 are executed by the controller302 after receiving the measurement values from the magnetic sensorarrays 604, 606.

Once the position of the magnetic source 309 relative to the magneticsensor arrays 604, 606 has been determined, the position data indicativethereof is transmitted to the controller 302. In addition, the angledata indicative of the angular displacement of the magnetic sensor array604, 606 and the distance data indicative of the linear displacement ofthe magnetic sensor array 604, 606 is transmitted to the controller 302via the communication link 326.

In response to the received data, the controller 302 determines theposition of the relevant bony anatomy of the patient. To do so, thecontroller 302 may execute an algorithm 720 as illustrated in FIG. 38.Similar to algorithm 420 illustrated in and described above in regard toFIG. 28, the algorithm 720 may be embodied as software or firmwarestored in, for example, the memory device 316. The algorithm 720 beginswith process step 722 in which the controller 302 receives the positiondata, the angle data, and the distance data from each of the magneticsensors 604, 606 via the communication link 326. As discussed above, theposition data is indicative of the position of the magnetic source 309(e.g., the magnets 450) relative to the respective magnetic sensor array604, 606. In the illustrative embodiment, the position data is embodiedas coefficient values that define the five degrees of freedom (i.e.,X-coordinate, Y-coordinate, Z-coordinate, (theta) θ-rotational, and(phi) φ-rotational) of the magnetic source 309 and thereby the bonyanatomy to which the magnetic source 309 is coupled. However, othertypes of position data that define the location and orientation of themagnetic source 309 and bony anatomy may be used in other embodiments.Once the data is received from the magnetic sensor arrays 604, 606, thecontroller 302 may store the position data, angle data, and distancedata in the memory device 316.

In process step 724, the controller 302 determines the position of theapparatus 600. To do so, the controller 302 receives images from thecamera unit 304 via the communication link 310. By analyzing theposition of the reflective sensor array 630 in the images, thecontroller 302 determines the position of the magnetic sensor apparatus600 relative to a reference point such as, for example, the camera 304and/or the controller 302.

Subsequently, in process step 726, the controller 302 determines theposition of the magnetic source 309 with respect to the computerassisted orthopaedic surgery (CAOS) system 301. To do so, the controller302 uses the position data indicative of the position of the magneticsource 309 relative to the magnetic sensor arrays 604, 606, the angledata indicative of the angular displacement of the magnetic sensorarrays 604, 606 from the vertical reference axis 670, the distance dataindicative of the linear displacement of the magnetic sensor arrays 604,606 from a reference point such as the coupler 608, and the position ofthe apparatus 600 determined in process step 424. That is, because thecontroller 302 has determined the position of the apparatus 600 withinthe coordinate system of the computer assisted orthopaedic surgery(CAOS) system 301, the controller 302 can determine the position of themagnetic sensor arrays 604, 606 in the same coordinate system based onthe angle data and distance data using an appropriate algorithm such asa vector addition algorithm. Similarly, because the magnetic sensorarrays 604, 606 have determined the position of the magnetic source 309relative to the arrays 604, 606 themselves, the controller 302 candetermine the position of the magnetic source 309 in the coordinatesystem of the computer assisted orthopaedic surgery (CAOS) system 301(i.e., with respect to the CAOS system 301) by combining the positiondata of the magnetic sensor arrays 604, 606 within the coordinate systemand the position data of the magnetic source 309 relative to themagnetic sensor arrays 604, 606 using an appropriate algorithm (e.g., avector addition algorithm).

Subsequently, in process step 728, the controller 302 retrieves thethree-dimensional image of the bony anatomy that was previouslygenerated. To do so, the controller 302 may retrieve the image from thedatabase 318 and/or from the remote database 320. The image may be soretrieved based on any suitable criteria. For example, in oneembodiment, the image is retrieved based on patient identification data.In such embodiments, the patient identification data may be supplied tothe controller prior to the performance of the orthopaedic surgicalprocedure. The controller may retrieve any number of generated images.The generated images include indicia or images of the magnetic source309 (e.g., the two magnets 450) and its position with respect to thebony anatomy.

In process step 730, the controller 302 creates a graphically renderedimage of the bony anatomy having a location and orientation based on theposition of the magnetic source 309 determined in process step 726 andsurface contours based on the image(s) of the bony anatomy retrieved inprocess step 728. However, because only five degrees of freedom of themagnetic source 309 were determined and transmitted to the controller302, the controller 302 must determine the sixth degree of freedom ofthe magnetic source 309. In some embodiments, the sixth degree offreedom is already determined or known by the controller 302. Forexample, in embodiments wherein the magnets 450 are implanted into therelevant bone(s) at a predetermined angle with respect to each other,such predetermined angle may be supplied to the controller 302 as thesixth degree of freedom. Alternatively, in embodiments wherein thethree-dimensional image(s) of the relevant bony anatomy and magneticsource 309 is determined using the algorithm 800 described above inregard to FIG. 25, the 1×5 matrix including the three components of thetranslation vector between the centroids of the magnets 450 and twoangular rotations defining the spatial relationship between the twomagnets 450 may have been determined in process step 810. However, evenif the matrix has not been previously determined, the controller 302 maybe configured to determine the matrix in process step 750. To do so, thecontroller 302 may execute the algorithm 850 described above in regardto and illustrated in FIG. 28.

Once the six degrees of freedom of the magnetic source 309 has beendetermined, the rendered image of the bony anatomy may be generated inprocess step 750 based on the six degrees of freedom of the magneticsource 309 and the data indicative of the positional relationshipbetween the magnetic source and the bony anatomy as determined inprocess step 808 of algorithm 800. That is, because the six degrees offreedom of the magnetic source 309 is known and the positionalrelationship between the bony anatomy and the magnetic source 309 isknown, the six degrees of freedom of the bony anatomy may be determinedby, for example, simple vector addition. The rendered image may bedisplayed to the surgeon or other user of the CAOS system 300 on thedisplay device 306 using the communication link 312.

Referring back to algorithm 700 in FIG. 37, after the bony anatomy hasbeen registered in process step 712, the magnetic source 309 may bedecoupled from the bony anatomy of the patient in process step 714. Todo so, the magnetic sensor arrays 604, 606 may be used to determine thelocation of the individual magnets 450 which form the magnetic source309. For example, the magnetic sensor arrays 604, 606 may be passed overthe skin of the patient until the indicators 680 of the magnetic sensorarrays 604, 606 are activated, which indicates that the magnetic sensorarrays 604, 606 are in the respective magnetic field of the magnets 450.The individual magnets 450 may then be removed using an appropriatesurgical procedure. In other embodiments, such as those embodimentswherein the sensor arrays 54 are embodied as wireless transmitters(i.e., electromagnetic sensor arrays) rather than reflective sensorarrays, the magnetic source 309 may be decoupled from the bone(s) of thepatient prior to the performance of the orthopaedic surgical procedureso as to avoid any magnetic interference with the operation of thesensor arrays 54. Again, however, if the magnetic source 309 is leftcoupled to the bone(s) of the patient during the performance of theorthopaedic surgical procedure, the bone(s) may be reregistered at anytime and as often as necessary during the procedure.

In process step 716, the orthopaedic surgical procedure is performed.The orthopaedic surgical procedure is performed using the images of therelevant bony anatomy generated in process step 73 of algorithm 720,which is displayed on the display device 306 in a position andorientation based on the position data, angle data, and distance datareceived from the magnetic sensor arrays 604, 606 and the generatedimages of the bony anatomy having indicia of the position of themagnetic source coupled therewith. The surgeon may use the system 300 tonavigate and step through the orthopaedic surgical process in a similarmanner as the CAOS system 10 illustrated in and described above inregard to FIGS. 1-17. For example, navigation with respect to the bonyanatomy may be facilitated by the use of a reflective sensor array, suchas one similar to the tibial array 60 of FIG. 3, coupled to the bonyanatomy. It should be appreciated, however, that the present algorithm700 for registering the bone anatomy of a patient may partially orcompletely replace the process step 106 of the algorithm 100 illustratedin and described above in regard to FIG. 6.

While the disclosure has been illustrated and described in detail in thedrawings and foregoing description, such an illustration and descriptionis to be considered as exemplary and not restrictive in character, itbeing understood that only illustrative embodiments have been shown anddescribed and that all changes and modifications that come within thespirit of the disclosure are desired to be protected.

There are a plurality of advantages of the present disclosure arisingfrom the various features of the systems and methods described herein.It will be noted that alternative embodiments of the systems and methodsof the present disclosure may not include all of the features describedyet still benefit from at least some of the advantages of such features.Those of ordinary skill in the art may readily devise their ownimplementations of the systems and methods that incorporate one or moreof the features of the present invention and fall within the spirit andscope of the present disclosure as defined by the appended claims.

1. A method for determining a position of a magnetic source coupled to abone of a patient, the method comprising: (i) measuring a magnetic fieldgenerated by the magnetic source with a magnetic sensor array, themagnetic field being defined by a plurality of three-dimensionalmagnetic flux densities; (ii) generating first data indicative ofcomponents of the three-dimensional magnetic flux density of themagnetic source at a plurality of points in space based on the measuringstep; (iii) determining an estimated position of the magnetic source;(iv) calculating second data indicative of a theoretical value of thecomponents of the three-dimensional magnetic flux density of themagnetic source based on the estimated position; (v) calculating adifference between the first data and the second data; and (vi)repeating steps (iii)-(v) until the difference between the first dataand the second data is less than a predetermined minimum thresholdvalue.
 2. The method of claim 1, wherein the measuring step comprisesmeasuring an X-component and a Y-component of the three-dimensionalmagnetic flux density of the magnetic source at a point in space andpositioning the magnetic sensor array over a longitudinal axis of themagnetic source such that the X-component and Y-component measurementsare minimized.
 3. The method of claim 1, wherein generating first datacomprises generating voltage values indicative of an X-component value,a Y-component value, and a Z-component value of the three-dimensionalmagnetic flux density of the magnetic source at the plurality of pointsin space.
 4. The method of claim 1, wherein determining an estimatedposition comprises estimating an X-coordinate value, a Y-coordinatevalue, and a Z-coordinate value of the location of at least one magneticsensor of the magnetic sensor array with respect to the magnetic source.5. The method of claim 4, wherein determining an estimated positioncomprises estimating a first value indicative of an amount of rotationabout an X-axis of the magnetic source and a second value indicative ofan amount of rotation about a Y-axis of the magnetic source.
 6. Themethod of claim 1, wherein the estimating step comprises estimatingvalues for at least five degrees of freedom of the magnetic source. 7.The method of claim 1, wherein calculating second data comprisescalculating theoretical values of an X-component, a Y-component, and aZ-component of the three-dimensional magnetic flux density of themagnetic field at a point in space.
 8. The method of claim 1, whereincalculating second data comprises calculating a theoretical value of anX-component of the three-dimensional magnetic flux density of themagnetic field using the following equation:$B_{x} = \frac{\mu\quad{m\left\lbrack {\frac{3{x\begin{pmatrix}{{x\quad{\sin(\Theta)}{\cos(\Phi)}} +} \\{{y\quad\sin(\Theta){\sin(\Phi)}} + {z\quad{\cos(\Theta)}}}\end{pmatrix}}}{r^{2}} - {{\sin(\Theta)}{\cos(\Phi)}}} \right\rbrack}}{4\quad\pi\quad r^{3}}$wherein B_(x) is the theoretical value of the X-component, x is anX-coordinate value of the estimated position of a magnetic sensor of themagnetic sensor array with respect to the magnetic source, y is aY-coordinate value of a magnetic sensor with respect to the magneticsource, z is a Z-coordinate value of the estimated position of themagnetic sensor with respect to the magnetic source, Θ is a rotationalvalue about the X-axis of the estimated position of the magnetic source,Φ is a rotational value about the Y-axis of the estimated position ofthe magnetic source, μ is the permeability of free space, m is themagnetic strength of the magnetic source, and r=√{square root over(x²+y²+z²)}.
 9. The method of claim 1, wherein calculating second datacomprises calculating a theoretical value of a Y-component of thethree-dimensional magnetic flux density of the magnetic field using thefollowing equation:$B_{y} = \frac{\mu\quad{m\left\lbrack {\frac{3{y\begin{pmatrix}{{x\quad{\sin(\Theta)}{\cos(\Phi)}} +} \\{{y\quad\sin(\Theta){\sin(\Phi)}} + {z\quad{\cos(\Theta)}}}\end{pmatrix}}}{r^{2}} - {{\sin(\Theta)}{\sin(\Phi)}}} \right\rbrack}}{4\quad\pi\quad r^{3}}$wherein B_(y) is the theoretical value of the Y-component, x is anX-coordinate value of the estimated position of a magnetic sensor of themagnetic sensor array with respect to the magnetic source, y is aY-coordinate value of the estimated position of the magnetic sensor withrespect to the magnetic source, z is a Z-coordinate value of theestimated position of the magnetic sensor with respect to the magneticsource, Θ is a rotational value about the X-axis of the estimatedposition of the magnetic source, Φ is a rotational value about theY-axis of the estimated position of the magnetic source, μ is thepermeability of free space, m is the magnetic strength of the magneticsource, and r=√{square root over (x²+y²+z²)}.
 10. The method of claim 1,wherein calculating second data comprises calculating a theoreticalvalue of an Z-component of the three-dimensional magnetic flux densityof the magnetic field using the following equation:$B_{z} = \frac{\mu\quad{m\left\lbrack {\frac{3{z\begin{pmatrix}{{x\quad{\sin(\Theta)}{\cos(\Phi)}} +} \\{{y\quad\sin(\Theta){\sin(\Phi)}} + {z\quad{\cos(\Theta)}}}\end{pmatrix}}}{r^{2}} - {\cos(\Phi)}} \right\rbrack}}{4\quad\pi\quad r^{3}}$wherein B_(z) is the theoretical value of the Z-component, x is anX-coordinate value of a magnetic sensor of the magnetic sensor arraywith respect to the magnetic source, y is a Y-coordinate value of theestimated position of the magnetic sensor with respect to the magneticsource, z is a Z-coordinate value of the estimated position the magneticsensor with respect to the magnetic source, Θ is a rotational valueabout the X-axis of the estimated position of the magnetic source, Φ isa rotational value about the Y-axis of the estimated position of themagnetic source, μ is the permeability of free space, m is the magneticstrength of the magnetic source, and r=√{square root over (x²+y²+z²)}.11. The method of claim 1, wherein calculating a difference between thefirst data and the second data comprises calculating a differencebetween a measured X-component and an estimated X-component of thethree-dimensional magnetic flux density of the magnetic source at apoint in space, calculating a difference between a measured Y-componentand an estimated Y-component of the three-dimensional magnetic fluxdensity of the magnetic source at a point in space, and calculating adifference between a measured Z-component and an estimated Z-componentof the three-dimensional magnetic flux density of the magnetic source ata point in space.
 12. The method of claim 1, wherein calculating adifference between the first data and the second data comprisescalculating a sum of the squared difference between the first data andthe second data.
 13. The method of claim 12, wherein calculating the sumof the squared difference between the first data and the second datacomprises calculating the sum of the squared difference between thefirst data and the second data using the following equation:$F = {\sum\limits_{i = 0}^{n}{w_{i}\left( {B_{{th}_{i}} - B_{{me}_{i}}} \right)}^{2}}$wherein F is a weighted sum, n is the number of magnetic field strengthcomponents measured, w_(i) is a weighting factor for the ith measuredcomponent, B_(th) is a theoretical value of the ith measured component,B_(me) is a measured value of the ith measured component.
 14. The methodof claim 1, wherein calculating a difference between the first data andthe second data comprises calculating a sum of the weighted square rootsof the squared differences.
 15. The method of claim 12, whereindetermining the position of the magnetic source comprises using a localoptimization algorithm to determine a minimum value of the sum of thesquared difference between the first data and the second data byadjusting the estimated position.
 16. The method of claim 12, whereindetermining the position of the magnetic source comprises using a globaloptimization algorithm to determine a minimum value of the sum of thesquared difference between the first data and the second data byadjusting the estimated position.
 17. A method for determining aposition of a magnetic source coupled to a bone of a patient, the methodcomprising: measuring the three-dimensional magnetic flux densitycomponents of a magnetic field generated by the magnetic source at aplurality of points in space; calculating components of a theoreticalthree-dimensional magnetic flux density at each of the plurality ofpoints in space based on an estimated position of the magnetic source;and calculating a sum of the squared difference between the measuredthree-dimensional magnetic flux density components and the theoreticalthree-dimensional magnetic flux density components; and optimizing thesum such that the sum is reduced below a predetermined minimum thresholdvalue.
 18. The method of claim 17, wherein optimizing the sum comprisesdetermining a local minimum value of the sum by adjusting the estimatedposition and determining the position of the magnetic source based onthe local minimum value.
 19. The method of claim 17, wherein determiningthe position of the magnetic source comprises determining values of atleast five degrees of freedom of the magnetic source.
 20. A method fordetermining a position of a magnetic source relative to a magneticsensor array, the method comprising: measuring the three-dimensionalmagnetic flux density components of a magnetic field generated by themagnetic source using the magnetic sensor array at a plurality of pointsin space; determining an estimated position of the magnetic sourcerelative to the magnetic sensor array; calculating theoreticalthree-dimensional magnetic flux density components based on theestimated position at each of the plurality of points in space; andreducing a sum of the squared difference between the measuredthree-dimensional magnetic flux density components at each point inspace and the corresponding theoretical three-dimensional magnetic fluxdensity components by adjusting the estimated position until the sum isbelow a predetermined threshold value.